To make the crust: Beat the cream cheese and butter until fluffy, about a minute. Add flour and continue mixing for another 1-2 minutes. Shape the dough into a ball and wrap it in plastic. Refrigerate for 30-60minutes.

Heat olive oil in skillet. Add the minced garlic and cook until fragrant. Add the sausage and brown over medium heat, breaking it into small pieces as you go. Add mushrooms and cook until tender and fully cooked. Salt and pepper to taste. Remove from heat. Stir in cheese. Add the egg and mix well.

Pre-heat oven to 375°F (190°C).

Cut the chilled dough into 24 pieces. Flatten each piece to fit into the mini muffin pan and place into a mini muffin cups. Pour ½ teaspoon marinara sauce into each muffin cup. Add sausage mixture. Top it with extra cheese, if desired. Place one pepperoni on each tartlet. Bake for 15-20 minutes. Serve hot.