In a blender, combine the eggs, egg whites, milk, and tomato paste. Blend until smooth. Add the oregano, garlic powder, salt, 2 tablespoons of melted butter, and flour and blend on high speed for 2-3 minutes, until completely smooth. Transfer the batter to a liquid measuring cup with a pour spout and let rest at room temperature for 20 minutes.
Meanwhile, place the popover pan in the oven to preheat.
After resting, fold ¼ cup (30 g) Parmesan and ¼ cup (35 g) chopped pepperoni into the popover batter.
Remove the popover pan from the oven and brush ¼ teaspoon melted butter in each cup, then fill ¾ of the way full with batter. Sprinkle with the remaining pepperoni and remaining 1½ tablespoons Parmesan cheese.
Bake the popovers for 25-30 minutes, or until they appear puffed and dry (do not open the oven door to check).
Garnish the popovers with basil and serve immediately with warm marinara sauce alongside.