In a large skillet, heat 2 tablespoons of vegan butter or olive oil over medium-low heat. Add 3 sliced sweet onions and cook for 25–30 minutes, stirring occasionally until golden brown and soft. Drizzle in 1 tablespoon of agave syrup towards the end.

While the onions caramelize, drain 1 block (15 oz) of extra firm tofu, place in a blender. Add 2 tablespoons of nutritional yeast, 1 teaspoon of lemon juice, and 2–3 tablespoons of non-dairy milk. Blend until smooth and creamy.

In another skillet, melt 2 tablespoons of vegan butter over medium heat. Whisk in 3 tablespoons of all-purpose flour to create a roux. Gradually add 2.5 cups of non-dairy milk while whisking continuously for 2–4 minutes until thickened. Stir in 1 teaspoon of fresh thyme, 1/4 teaspoon of nutmeg, salt, and pepper to taste.

Preheat your oven to 375°F (190°C). Spread a layer of béchamel sauce at the bottom of a baking dish. Layer lasagna sheets, followed by ricotta, caramelized onions, and vegan mozzarella. Repeat layers, ending with lasagna sheets topped with remaining béchamel and mozzarella.

Bake the assembled lasagna for 25–30 minutes until bubbly and golden brown. Let cool for a few minutes before slicing.