Step 1: In a large mixing bowl, cream together the softened butter and cream cheese until light and fluffy. This should take about 2-3 minutes with an electric mixer.
Step 2: Gradually add the all-purpose flour to the cream cheese mixture, mixing on low speed until just combined and a soft dough forms. Do not overmix.
Step 3: Divide the dough into 24 equal pieces. Press each piece evenly into the bottom and up the sides of ungreased mini muffin cups. Chill the crusts in the refrigerator for at least 30 minutes while you prepare the filling.
Step 4: Preheat your oven to 350°F (175°C). In a separate medium bowl, whisk together the eggs, granulated sugar, and light brown sugar until well combined.
Step 5: Stir in the melted butter and vanilla extract into the egg mixture until smooth.
Step 6: Gently fold in the chopped pecans. Make sure the pecans are evenly distributed throughout the filling.
Step 7: Remove the chilled crusts from the refrigerator. Spoon about 1 tablespoon of the pecan filling into each prepared mini muffin cup.
Step 8: Bake for 20-25 minutes, or until the crusts are golden brown and the filling is set but still slightly jiggly in the center. The baking time may vary slightly depending on your oven.
Step 9: Remove the muffin tins from the oven and let the tassies cool in the tins for about 5-10 minutes before carefully transferring them to a wire rack to cool completely. This ensures they firm up and are easy to remove.