Dough: In a medium bowl, cream sugar, butter, vanilla extract and egg yolks until
light and fluffy. Lightly spoon flour into measuring cup; level off. Gradually add
flour and baking powder to creamed mixture, mixing well. Refrigerate 30 minutes.
Meanwhile, make the filling.
Heat oven to 350 degrees F.
Shape dough into 1-inch balls. Place 2 inches apart on ungreased baking sheet.
With thumb, make imprint in center of each cookie, and fill with 1/2 teaspoon filling.
Bake for 11 to 14 minutes, or until light golden brown around edges. Store in refrigerator.
Filling: In small saucepan, mix sugar, flour, and almond flavoring. Gradually
add eggnog and cook over low heat until smooth and thickened, stirring constantly.
In small bowl, blend 2 tablespoons hot mixture into slightly beaten egg yolk.
Return to saucepan; blend well. Cook just until mixture bubbles, stirring constantly.