How to Make It
Cook sausage in a 10-inch nonstick skillet over medium-high, breaking it up into small pieces with a wooden spoon, until browned, 5 to 6 minutes. Transfer sausage to a cutting board using a slotted spoon; discard fat. Let cool slightly, about 5 minutes, or until cool enough to handle. Chop sausage into small pieces.
Return sausage to skillet over medium-low; stir in mascarpone, Worcestershire, and oregano until smooth, about 3 minutes. Add Taleggio; gently cook, stirring often, until cheese is just melted and gooey, 4 to 5 minutes. Remove pan from heat; stir in 2 tablespoons parsley and salt. Let cool to room temperature, about 20 minutes. (The topping can be transferred to an airtight container and stored in refrigerator up to 3 days.)
Preheat oven to 350°F. Arrange bread slices on a large rimmed baking sheet with some space between them. Top each slice with about 1 1/2 teaspoons cheesy sausage mixture and 1 teaspoon fontina.
Bake in preheated oven until bread is toasted and topping is lightly browned, 18 to 20 minutes. Cut toasts in half; sprinkle with remaining 2 tablespoons parsley. Serve hot.