Step 1

Preheat oven to 350F with a rack in the center. Oil a 9x13-inch baking dish, or equivalent.

Step 2

If using, cook your plant-based sausage per package instructions (usually in a small amount of oil), until browned on both sides. Remove from skillet and place on paper towel until it has cooled a bit. Crumble and set aside.

Step 3

In a large bowl whisk together the mustard, cayenne, salt, milk, and eggs. Add half of the Gruyere cheese, the bagel segments and the cooked plant-based sausage. Toss until everything is well coated.

Step 4

Pour the mixture into the prepared baking dish. Sprinkle with the remaining Gruyere, then dot with crumbled pieces of the Boursin cheese. At this point you can either bake the casserole or refrigerate it, covered, overnight.

Step 5

When you’re ready to bake, sprinkle the casserole with the everything bagel seasoning. Cover with foil, poke a few holes in the foil with a fork, and bake for 45 minutes. Carefully remove the foil and bake for another 30-40 minutes, or perhaps a bit longer if you are baking straight from the refrigerator. The casserole should be beautifully golden when it is ready. Cool for 5-10 minutes before serving.