One-Skillet Butternut Sage Lasagna with Brown Butter Fontina Step-by-step instructions

Before you start

Before starting, gather all the ingredients and equipment. Peel and slice the butternut squash thinly, about 1/8-inch thick, and set aside. Grate the fontina and Parmesan, keeping them separate. Pick the sage leaves from the stems and have them ready.

Measure out the milk, butter, flour, salt, pepper, and nutmeg. Heat the oven to 400°F (200°C) and have a 10-inch cast iron skillet ready. No-boil lasagna noodles are essential—they soften in the béchamel as they bake, so there’s no need to boil them first.

Instructions

Prep and Roast

1. 1Prepare the Squash and Cheese
   Heat the oven to 400°F (200°C). Peel the butternut squash, cut it in half lengthwise, scoop out the seeds, and slice it thinly, about 1/8-inch thick. Set the slices aside. Pick the sage leaves from the stems and set aside. Grate the fontina cheese on the large holes of a box grater and grate the Parmesan finely. Keep them separate.
   Look for The squash slices are thin and even for quick roasting.
   Tip Use a mandoline for consistently thin squash slices.
2. 2Roast the Squash
   Spread the squash slices on a baking sheet in a single layer. Roast for 15 minutes, until just tender and lightly browned at the edges. Remove from the oven and set aside. Leave the oven on for baking the lasagna.
   Look for The squash is fork-tender but not mushy.
   Tip Roasting brings out the natural sweetness and concentrates flavor.

The squash slices are tender and lightly caramelized, and the cheese is grated and ready. The sage leaves are picked and set aside. The oven is preheated and the baking sheet is lined. Everything is organized for quick assembly.

Béchamel and Assembly

3. 3Make the Sage Brown Butter Béchamel
   In a medium saucepan over medium heat, melt the butter. Add the sage leaves and cook, stirring, until the butter foams and turns golden brown and the sage is fragrant, about 3 minutes. Sprinkle in the flour and whisk constantly for 1 minute. Slowly pour in the milk, whisking to prevent lumps. Cook, whisking, until the sauce thickens and coats the back of a spoon, about 5 minutes. Stir in salt, pepper, and nutmeg. Remove from heat.
   Look for The sauce is smooth and thick enough to coat a spoon.
   Tip Watch the butter carefully—it can go from brown to burnt quickly.
4. 4Layer the Lasagna
   Spread a thin layer of béchamel on the bottom of a 10-inch cast iron skillet. Arrange 4 lasagna noodles over the sauce, breaking them to fit if needed. Layer with half of the roasted squash, a third of the remaining béchamel, and a third of the fontina. Repeat with another layer of noodles, the remaining squash, half of the remaining béchamel, and half of the remaining fontina. Top with the last noodles, the rest of the béchamel, and the rest of the fontina.
   Look for The layers are even and the top is covered with sauce and cheese.
   Tip Press the noodles down gently to ensure they are submerged in the sauce.

The béchamel is smooth, thick, and aromatic with sage and nutmeg. The skillet is layered evenly with noodles, squash, sauce, and cheese, with the top fully covered. The layers are even and the noodles are nestled into the sauce.

Bake and Finish

5. 5Bake Until Golden and Blistered
   Place the skillet in the oven and bake for 25 to 30 minutes, until the top is golden and the cheese is bubbling and blistered in spots. Let the lasagna rest for 10 minutes before serving.
   Look for The sauce is bubbling and the cheese is browned and blistered.
   Tip For extra blistering, switch to the broiler for the last 2 minutes.
6. 6Garnish and Serve
   While the lasagna rests, heat a small skillet with a little oil over medium heat. Add the remaining sage leaves and fry until crisp, about 30 seconds per side. Drain on paper towels. Sprinkle the lasagna with the crispy sage leaves and the remaining grated Parmesan. Cut into wedges and serve hot, pulling up a portion to show the cheese stretch.
   Look for The sage is crisp and the Parmesan is fresh.
   Tip Frying the sage in the same brown butter adds extra flavor.

The top is golden and blistered, with the cheese bubbling at the edges. The lasagna is set after resting, and the crispy sage leaves and Parmesan add a final touch. The aroma of brown butter and sage fills the kitchen.

Common mistakes

One common mistake is slicing the butternut squash too thick, which makes it hard to layer and may leave it undercooked. Aim for thin, even slices—a mandoline helps. Another pitfall is not whisking the béchamel enough, leading to lumps.

Whisk constantly when adding the milk and keep the heat moderate. Also, don’t skip the resting time; cutting into the lasagna too soon causes it to fall apart. Finally, be careful not to over-brown the butter—it should be golden and nutty, not dark and bitter.

How to tell it’s done

The lasagna is done when the top is golden brown and the cheese is bubbling and blistered in spots.

The edges should be crisp and browned, and the center should be hot and bubbly. To check, insert a knife into the center—it should come out hot and the noodles should be tender.

If the top is browning too quickly, cover loosely with foil. After removing from the oven, let it rest for 10 minutes; this allows the layers to set and makes slicing easier. The internal temperature should be at least 165°F (74°C) if you want to be precise.