1. Make the pepperoni butter: In a food processor, combine the butter, pepperoni, smoked paprika, and red pepper flakes and process until well combined. The final mixture should be semi-smooth.
2. Make the toast: Spread a generous amount of the pepperoni butter over each slice of bread. Position an oven rack in the top third of the oven, 3-5 inches (7.5-10 cm) from the broiler (grill) element, and preheat to high. If you have an old-school broiler drawer beneath your oven, you can get a better result by setting the baking sheet on top of a muffin tin, thereby elevating the baking sheet to 2-3 inches (5-7.5 cm) from the heating element. Set the bread on a foil-lined baking sheet and broil until golden brown, about 2-3 minutes (watch the bread closely as broiler intensities vary--never walk away from food under the broiler!). Flip the bread slices and toast the other side until golden brown, another 1-2 minutes.
3. Place 2 pieces of mozzarella over each bread slice (overlapping if necessary), set on the baking sheet, and broil until the cheese is melted and browned, 2-3 minutes (watch the cheese closely as the broiler intensities vary).
4. To serve, top each toast with 1 tablespoon basil and sprinkle with salt.
"Toast: The Cookbook" by Raquel Pelzel (c) Phaidon Press 2015. Provided courtesy of Raquel Pelzel. All rights reserved.