In a large mixing bowl, beat butter, cream cheese, and sugar on medium speed until light and fluffy. Add egg yolk, extract, and salt. Beat on low speed until combined. Use a wooden spoon to gradually stir in flour until well mixed.
Chill dough for 30 minutes.
Preheat oven to 325 degrees.
Spray a large cookie sheet with no-stick cooking spray. Shape dough into 1-inch balls and place 2-inches apart on cookie sheet. Press thumb into center of each cookie, making indentions large enough to fill with ½ teaspoon of almond paste. Fill each with almond paste.
Bake for 14-16 minutes just until edges are golden. Makes 4 dozen.