In a small bowl, combine the poppy seed filling and lemon juice; set aside. In a large bowl, cream butter and sugar until light and fluffy. Beat in the egg yolks, lemon zest and extracts. Combine the flour, baking powder and baking soda; gradually add to creamed mixture alternately with buttermilk, beating well after each addition.
Drop by tablespoonfuls onto greased baking sheets. Using the end of a wooden spoon handle, make an indentation about 1/2 in. deep in the center of each. Fill with about 1/2 teaspoon of poppy seed filling. Top with a teaspoonful of dough.
Bake at 350° for 14-16 minutes or until edges are golden brown. Remove to wire racks to cool.
For frosting, in a large bowl, beat the confectioners' sugar, butter, milk, extract and lemon zest until blended. Spread over cookies. Sprinkle with poppy seeds if desired.