Caramelized Onion and Mushroom Flatbread with Fontina and Thyme

Why You’ll Love This Recipe

• Restaurant-level flavor with weeknight-friendly shortcuts thanks to store-bought naan.
• Deeply caramelized onions and garlicky mushrooms meet oozy fontina and fresh thyme.
• A glossy balsamic swipe adds tangy-sweet balance to every bite.
• Versatile: serve as an appetizer, light dinner, or pair with salad and soup.

Grocery List

• Produce: Yellow onions, cremini mushrooms, garlic, fresh thyme, lemon (optional)
• Dairy: Fontina cheese, Parmesan (optional), unsalted butter, naan (check bakery/deli)
• Pantry: Balsamic vinegar, honey, olive oil, kosher salt, black pepper, red pepper flakes (optional)

Full Ingredients

Caramelized Onions

• 2 medium yellow onions (about 1 lb), halved and thinly sliced pole-to-pole
• 1 tbsp unsalted butter
• 1 tbsp olive oil
• 1/2 tsp kosher salt
• 1–2 tbsp water, as needed to deglaze

Garlicky Mushrooms

• 16 oz cremini (baby bella) mushrooms, trimmed and sliced 1/4 inch
• 2 tbsp olive oil
• 3 cloves garlic, minced
• 1 tsp fresh thyme leaves, plus more for garnish
• 1/2 tsp kosher salt
• 1/4 tsp freshly ground black pepper
• 1 tsp lemon juice (optional, to brighten)

Balsamic Swipe

• 1/2 cup balsamic vinegar
• 1 tsp honey

To Assemble and Finish

• 2 naan (8–9 inch)
• 1 1/2 cups shredded fontina cheese (about 6 oz)
• 2 tbsp finely grated Parmesan (optional)
• 2 tsp olive oil (for brushing naan edges)
• Flaky salt and red pepper flakes (optional), to finish

Step-by-Step Instructions

Step 1: Preheat the oven and pan

Place a rimmed baking sheet or pizza stone on the middle rack and preheat the oven to 475°F for at least 15 minutes. A hot surface helps the naan crisp and the cheese bubble beautifully.

Step 2: Caramelize the onions

Heat a large skillet over medium-low. Add the butter and 1 tbsp olive oil. Stir in the sliced onions and 1/2 tsp kosher salt. Cook, stirring every few minutes, until the onions turn deeply golden and jammy, 25–30 minutes. If brown bits build up, add 1–2 tbsp water to deglaze and keep them glossy. Transfer to a bowl.

Step 3: Sauté the mushrooms with garlic and thyme

Return the skillet to medium-high heat. Add 2 tbsp olive oil and the sliced mushrooms in an even layer. Cook undisturbed for 3 minutes to sear, then stir and continue cooking until browned and the pan is mostly dry, 3–5 minutes more. Reduce heat to medium, add garlic and thyme, and cook 30–60 seconds until fragrant. Season with 1/2 tsp kosher salt, 1/4 tsp black pepper, and lemon juice if using. Remove from heat.

Step 4: Make the balsamic reduction

In a small saucepan, combine balsamic vinegar and honey. Bring to a simmer over medium heat and cook, swirling occasionally, until reduced by about half and syrupy enough to lightly coat a spoon, 6–10 minutes. It will thicken further as it cools. Set aside.

Step 5: Build the flatbreads

Brush the outer edges of each naan with 2 tsp olive oil total. Swipe 1 tbsp warm balsamic reduction across the center of each naan (save the rest for finishing). Sprinkle half the fontina over the balsamic, then evenly distribute the caramelized onions and mushrooms. Top with remaining fontina and the Parmesan, if using.

Step 6: Bake until bubbly

Carefully slide the assembled naan onto the preheated sheet or stone. Bake at 475°F until the cheese is melted and bubbling and the naan edges are crisp and browned, 7–9 minutes. For extra blistering, broil for 30–60 seconds, watching closely.

Step 7: Finish and serve

Drizzle or flick a little more balsamic reduction over the hot flatbreads. Sprinkle with fresh thyme, a pinch of flaky salt, and red pepper flakes if desired. Slice and serve immediately.

Pro Tips

• Dry sear mushrooms first: spacing them out and not stirring for the first few minutes helps develop browning instead of steaming.
• Cook onions low and slow: medium-low heat is key to deep caramelization without burning. A splash of water rescues any hot spots.
• Hot surface, crisp base: preheating a sheet pan or stone gives naan that pizzeria-like crunch.
• Cheese as glue: a little cheese under and over the toppings locks everything in place.
• Don’t over-reduce balsamic: aim for warm maple-syrup thickness; if it gets too thick, whisk in 1–2 tsp hot water.

Variations

• Goat cheese swirl: Dot 2–3 oz soft goat cheese on top before baking for creamy tang.
• Prosciutto and arugula: Add torn prosciutto after baking and shower with a handful of arugula tossed in lemon and olive oil.
• Truffle and taleggio: Swap fontina for taleggio and finish with a few drops of white truffle oil.

Storage & Make-Ahead

Caramelized onions keep 4–5 days refrigerated or up to 1 month frozen. Cooked mushrooms keep 3 days refrigerated. Balsamic reduction lasts 2 weeks in an airtight jar. Assemble and bake flatbreads just before serving for best texture. Leftover baked slices keep 2 days refrigerated; reheat at 375°F on a sheet pan for 8–10 minutes until hot and crisp. Freezing assembled flatbreads is not recommended due to moisture from the mushrooms and onions.

Nutrition (per serving)

Approximate: 510 calories; 28 g fat; 48 g carbohydrates; 19 g protein; 3 g fiber; 720 mg sodium. Values will vary based on brands and exact portions.