Beat Cream Cheese (4 ounce) and Unsalted Butter (2 tablespoon) for about 1 minute until well blended.
Add All-Purpose Flour (3/4 cup) and continue mixing for another 1-2 minutes.
Shape the dough into a ball and wrap it in plastic. Refrigerate for 30-60 minutes.
Heat Olive Oil (1 tablespoon) in a pan and add a Garlic (1 clove). Add chopped Italian Sausage (2) and brown over medium heat.
Add in Mushroom (4 ounce) and cook until tender.
Add Salt and Pepper (to taste). Remove from heat. Stir in Cheese (1/2 cup).
Beat Egg (1) and pour into sausage mixture.
Preheat oven to 375 degrees F (190 degrees C).
Cut the chilled dough into 24 pieces. Flatten each piece a little and place into a mini muffin pan. Pour 1/2 teaspoon of Marinara Sauce (1/2 cup) into each muffin cup. Add sausage mixture.
Top with extra cheese, if desired. Place one Mini Pepperoni (24) on each tartlet. Bake for 15-20 minutes.