In a large bowl, cream butter and sugars until light and fluffy, about 5 minutes. Add eggs and extract; mix well. Add flour and baking powder (dough will be soft). Chill.
For filling, in a small bowl, stir egg white, sugar, almonds and lemon juice. Remove a portion of the dough at a time from the refrigerator. Place 1-in. balls of dough into miniature muffin cups, pressing slightly into sides and bottom. Place 1/2 teaspoon filling into each. Cover with quarter-sized circles of dough.
Brush with a little milk and top with an almond. Bake at 350° until golden, 14-16 minutes.