In a large bowl, beat together the Cream Cheese (8 ounce), All-Purpose Flour (1 1/2 cup), and Butter (1/2 cup) to form a dough. Chill for one hour.
Preheat the oven to 450 degrees F (230 degrees C). Add the Mushroom (0.5 pound) to the bowl of a food processor and pulse until finely minced and transfer to a large skillet.
Add the Butter (3 tablespoon) to the skillet and cook over medium-high heat, until the mushrooms give off some of their liquid.
Add the Onion (1) to the food processor and pulse until finely minced.
Add onions to the mushroom mixture. Cook until the onions have cooked and softened, about 5 to 7 minutes.
Stir in the Sour Cream (1/4 cup), Salt (1 teaspoon) and Dried Thyme (1/4 teaspoon). Cook for about a minute until thickened and remove from heat to cool.
Meanwhile, roll out the dough and cut into about 2 3⁄4-inch circles and press into a mini muffin pan.
Fill the pastry cups with 1 teaspoon of mushroom filling.
Bake for 12-14 minutes or until the crust is a light golden brown.