Preheat oven to 375°F with a rack in the upper third. Lightly grease a large baking dish. Coarsely chop roasted red peppers. Trim ends from scallions, then thinly slice. In a liquid measuring cup, stir together 1 cup milk and 2 teaspoons vinegar; set buttermilk aside for step 4.

Heat 2 teaspoons oil in a large nonstick skillet over medium-high. Add chorizo and cook, breaking up into smaller pieces, until browned, 5–7 minutes. Stir in peppers and ⅔ of the scallions. Transfer chorizo mixture to prepared baking dish.

In a large bowl, whisk 8 large eggs and all of the mascarpone until combined, then stir in 1½ cups water, 1 teaspoon salt, and a few grinds of pepper. Pour egg mixture evenly over chorizo mixture.

Place 8 tablespoons (1 stick) butter in a large microwave-safe bowl and microwave until melted (or melt in a small pot over medium heat, then transfer to a large bowl). Add buttermilk and stir to combine. Using a fork, gently stir in self-rising flour and ½ teaspoon salt until just combined. Gently stir in half of the shredded cheddar.

Using a tablespoon, drop biscuit dough over egg mixture (it will not be completely covered). Top with remaining shredded cheddar and a few grinds of pepper. Bake on upper oven rack until biscuits are golden and cooked through and egg mixture is set, about 30 minutes. Let sit 5 minutes. Top cheddar biscuit bake with remaining scallions before serving. Enjoy!

Give this brunch bake a drizzle of maple syrup or your favorite hot sauce before serving, whichever you prefer!