Prepare the Dough:

Beat softened butter and cream cheese in a bowl until smooth and creamy.

Mix in the egg yolk, then gradually add the flour until a soft dough forms.

Cover the dough and refrigerate for 30 minutes to firm up.

Make the Filling:

Whisk together melted butter and eggs in a bowl.

Stir in brown sugar and vanilla until smooth.

Fold in the chopped pecans.

Assemble the Tassies:

Preheat the oven to 350°F (175°C).

Grease mini muffin tins or line with paper liners.

Roll the dough into 1-inch balls and press each into the muffin cups, shaping a shell.

Fill each shell with the pecan filling, leaving a small gap at the top.

Bake:

Bake for 20-25 minutes, or until the filling sets and the crust turns golden.

Cool in the pan for 10 minutes, then transfer tassies to a wire rack to cool completely.