A savory, high-protein brunch bake with toasted bagels, sharp cheddar, plant-based sausage, and a custardy egg base, finished with tangy pockets of cream cheese. Topped with everything bagel seasoning for a crunchy, aromatic finish that delights a crowd.
Preheat oven to 375°F (190°C). Generously butter a 9x13-inch (23x33 cm) casserole dish and set aside.
Slice bagels in half, tear into bite-sized pieces (about 1.5 inches/4 cm), spread on a baking sheet, and toast until edges are golden and slightly crisp, 5 to 7 minutes.
Heat a large nonstick skillet over medium heat. Melt 1 tablespoon butter, crumble in the plant-based sausages, and cook until browned and cooked through, 6 to 8 minutes.
In a large bowl, whisk eggs. Add milk, dijon mustard, salt, and black pepper; whisk thoroughly to combine.
Stir in toasted bagel pieces, cooked sausage, 1 1/2 cups of the shredded cheddar, and sliced scallions until evenly mixed.
Transfer mixture to the greased casserole dish. Top with the remaining 1/2 cup shredded cheddar. Cut cream cheese into small cubes (about 1/2 inch/1.5 cm) and scatter over top. Sprinkle with everything bagel seasoning.
Cover tightly with foil and bake for 30 minutes. Remove foil and continue baking until the center is set and edges are deeply golden, 30 to 45 minutes more.
Let rest 5 to 10 minutes before serving. Garnish with extra sliced scallions, if desired.