Preheat the oven to 400º.

Spray or use cupcake liners on 12 muffin tins.

In a large bowl, mix the sugar and lemon peel.

Add in the flour, baking powder, baking soda, salt, and poppy seeds just until mixed. Do not overmix. Set aside.

In a small bowl, combine the sour cream eggs, vanilla extract, lemon extract, lemon juice, and melted butter. Add this to the flour mixture and mix just until well-blended. Do not overmix.

Pour the batter into the prepared muffin tins.

Bake at 400º for 18 minutes or until a cake tester inserted in the center of a muffin comes out clean.

Immediately remove the muffins from the tin and cool them on a wire rack.

When muffins are cooled, use a sharp knife to cut a circle into the top of the muffin, going down about half-way in the muffin. Remove the top.

Fill the cavity with lemon filling.

Cut off the cake part of the top piece you cut out and replace the cut-out circle top over the filling, pushing it down a little into the filling.

Store the muffins covered in the refrigerator.