Quick Recipe Version (TL;DR)
Quick Ingredients
- 4 large portobello mushroom caps (about 4 to 5 inches wide)
- 4 oz (115 g) low-moisture mozzarella, shredded
- 4 oz (115 g) Muenster, shredded
- 1 cup (125 g) all-purpose flour
- 2 large eggs + 2 tbsp water
- 2 cups (100 g) panko breadcrumbs
- 1 tsp kosher salt, 1 tsp garlic powder, 1/2 tsp smoked paprika, 1/4 tsp black pepper
- 6 cups (1.4 L) neutral frying oil; fry at 350°F (175°C)
- 4 potato buns + 2 tbsp butter (to toast)
- Shack-style sauce: 1/2 cup mayo, 2 tbsp ketchup, 1 tsp Dijon, 1 tbsp pickle brine, 1 tbsp dill relish, 1/4 tsp garlic powder
- 4 lettuce leaves + 1 large tomato (4 slices)
Do This
- 1) Stir together the Shack-style sauce; chill.
- 2) Clean mushrooms, remove stems/gills, and stuff each cap with the mozzarella–Muenster mix; freeze 10 minutes.
- 3) Set up breading stations: seasoned flour, egg wash, and panko.
- 4) Bread each stuffed cap (flour → egg → panko), pressing firmly; chill 10 minutes.
- 5) Fry at 350°F (175°C) for 3 to 4 minutes, flipping once, until deep golden; drain 2 minutes.
- 6) Toast buttered potato buns, then stack sauce + lettuce + tomato + fried ’shroom; serve hot.
Why You’ll Love This Recipe
- Gooey, stretchy cheese inside a crisp, crunchy panko crust—just like the famous original.
- A realistic home-cook method with easy grocery-store ingredients.
- Shack-style sauce brings that tangy, slightly sweet, peppery “burger stand” flavor.
- Make-ahead friendly: you can stuff and bread the mushrooms before guests arrive.
Grocery List
- Produce: 4 large portobello mushroom caps, 1 head green leaf lettuce (or iceberg), 1 large tomato
- Dairy: low-moisture mozzarella (shredded), Muenster (shredded), butter, mayonnaise
- Pantry: all-purpose flour, panko breadcrumbs, ketchup, Dijon mustard, dill pickle relish, pickle brine (from the jar), garlic powder, smoked paprika, kosher salt, black pepper, neutral frying oil (canola/peanut/vegetable), potato buns
Full Ingredients
Shack-Style Sauce
- 1/2 cup (120 g) mayonnaise
- 2 tbsp (30 g) ketchup
- 1 tsp Dijon mustard
- 1 tbsp dill pickle relish
- 1 tbsp pickle brine (juice from the pickle jar)
- 1/4 tsp garlic powder
- 1/8 tsp smoked paprika
- 1/8 tsp kosher salt (optional; add only after tasting)
- 1/8 tsp freshly ground black pepper
Stuffed Portobellos
- 4 large portobello mushroom caps (about 4 to 5 inches wide)
- 4 oz (115 g) low-moisture mozzarella, shredded
- 4 oz (115 g) Muenster, shredded
- 1/4 tsp kosher salt
- 1/4 tsp black pepper
Breading
- 1 cup (125 g) all-purpose flour
- 1 tsp kosher salt
- 1 tsp garlic powder
- 1/2 tsp smoked paprika
- 1/4 tsp freshly ground black pepper
- 2 large eggs
- 2 tbsp water
- 2 cups (100 g) panko breadcrumbs
For Frying
- 6 cups (1.4 L) neutral oil (canola, peanut, or vegetable), for deep frying
For Serving
- 4 potato buns
- 2 tbsp (28 g) butter, softened (for toasting buns)
- 4 crisp lettuce leaves (green leaf, romaine, or iceberg)
- 1 large tomato, cut into 4 thick slices
- 1/4 tsp kosher salt (for seasoning tomato slices)
Step-by-Step Instructions
Step 1: Make the Shack-style sauce
In a small bowl, whisk together the mayonnaise, ketchup, Dijon mustard, relish, pickle brine, garlic powder, smoked paprika, black pepper, and (optional) salt.
Cover and refrigerate while you prep everything else. (Even 20 minutes of chilling helps the flavors meld.)
Step 2: Prep the mushrooms for stuffing
Gently wipe the portobello caps clean with a damp paper towel. Twist off the stems.
Using a spoon, scrape out the dark gills to create a shallow cavity (this also helps prevent the burger from turning grey inside). Try not to gouge too deeply—keep the cap sturdy.
Pat the mushrooms very dry on the inside and outside with paper towels. Moisture is the enemy of crisp breading.
Step 3: Stuff with the mozzarella–Muenster mix
In a bowl, toss together the shredded mozzarella, shredded Muenster, 1/4 tsp kosher salt, and 1/4 tsp black pepper.
Flip each mushroom cap gill-side up. Pack about 1/2 cup of the cheese mixture into each cap, mounding it slightly. Press it in firmly so it holds together.
Place the stuffed caps on a plate or small tray and freeze for exactly 10 minutes. This quick chill firms the cheese so it stays inside while frying.
Step 4: Set up a tidy breading station
Set out three wide, shallow bowls (or pie plates):
Bowl 1 (seasoned flour): Whisk together the flour, 1 tsp kosher salt, garlic powder, smoked paprika, and black pepper.
Bowl 2 (egg wash): Beat the eggs with 2 tbsp water until smooth.
Bowl 3 (crumbs): Add the panko.
Line a baking sheet with parchment paper (or a rack) for the breaded mushrooms.
Step 5: Bread the stuffed mushrooms (press firmly)
Working with one stuffed mushroom at a time, keep one hand for dry and one hand for wet if you can (it helps avoid clumps):
Coat the mushroom all over in the seasoned flour, including the sides. Tap off excess.
Dip into the egg wash and let the extra drip off.
Press into the panko, coating the top, bottom, and sides well. Use your palms to gently press crumbs onto the mushroom so the crust adheres.
Set on the lined baking sheet and repeat with the remaining mushrooms.
Refrigerate the breaded mushrooms for 10 minutes. This helps the coating “set” and reduces blowouts in the fryer.
Step 6: Fry until crisp outside and gooey inside
In a heavy-bottomed pot or Dutch oven (at least 5 to 6 quarts), heat 6 cups neutral oil to 350°F (175°C). Use a thermometer for accuracy.
Carefully lower in 1 to 2 mushrooms at a time (don’t crowd the pot). Fry for 3 to 4 minutes total, flipping once halfway through, until deep golden brown.
Keep the oil between 340°F and 355°F (170°C to 180°C). If it drops too low, the coating can absorb oil and turn greasy.
Remove with a spider strainer or slotted spoon and drain on a wire rack (best) or paper towels for 2 minutes. Repeat with remaining mushrooms, letting the oil return to 350°F (175°C) between batches.
Step 7: Toast the buns and assemble the burgers
Lightly butter the cut sides of the potato buns with the softened butter. Toast in a skillet over medium heat for 1 to 2 minutes, until golden.
Season the tomato slices with 1/4 tsp kosher salt (a pinch per slice).
To assemble each burger: spread about 1 tbsp sauce on the bottom bun, add lettuce, add a tomato slice, set the hot fried ’shroom on top, then spread another 1 tbsp sauce on the top bun and close.
Serve immediately while the cheese is molten and stretchy.
Pro Tips
- Dry mushrooms = crispier crust. After scraping the gills, pat very dry. If your mushrooms are extra wet, let them sit uncovered in the fridge for 20 minutes before stuffing.
- Chill twice to prevent cheese leaks. Freeze the stuffed caps for 10 minutes, then chill again after breading for 10 minutes.
- Press the panko on firmly. A loose coating is the main reason breading falls off during frying.
- Use a thermometer. Holding the oil at 350°F (175°C) gives you a crisp shell without greasy crumbs.
- Drain on a rack. Airflow keeps the crust crunchy better than paper towels alone.
Variations
- Extra “Shack” tang: Add 1/2 tsp white vinegar to the sauce and an extra 1 tsp relish.
- Spicy ’Shroom: Add 1/4 tsp cayenne to the seasoned flour and stir 1 tsp hot sauce into the egg wash.
- Oven/air-fryer method (less authentic but workable): Spray breaded mushrooms generously with oil spray. Bake on a rack at 425°F (220°C) for 18 to 22 minutes, flipping once, until deep golden. The cheese will be melty, but the crust won’t be quite like deep-fried.
Storage & Make-Ahead
Best eaten right away: This burger is at its peak within 10 minutes of frying.
Make-ahead: You can stuff the mushrooms up to 24 hours ahead; keep covered in the fridge. You can also bread them up to 4 hours ahead; refrigerate uncovered on a rack so the coating stays dry.
Leftovers: Store fried mushrooms (separately from buns/veg/sauce) in an airtight container in the fridge for up to 2 days. Re-crisp on a rack in a 400°F (205°C) oven for 10 to 12 minutes. (Microwaving will soften the crust.)
Sauce: Keeps refrigerated for up to 5 days.
Nutrition (per serving)
Approximate, per 1 assembled burger: 840 calories, 44 g fat, 78 g carbs, 30 g protein, 1,420 mg sodium. Values vary by bun size, oil absorption, and exact cheese brands.
