Preheat oven to 350 degrees. Butter a standard 6-cup muffin tin; set aside. In a medium bowl, beat butter, granulated sugar, and zest until light and fluffy. Beat in egg yolks one at a time until creamy; set aside. Into a small bowl, sift together flour, baking powder, and salt. Add flour mixture and milk in alternating batches to butter mixture; set aside.
In a clean bowl, whisk egg whites to soft peaks; fold into batter. Divide half of batter among muffin cups. Make an indentation in the middle of each; fill with 1 tablespoon jam. Top with remaining batter.
Bake until a cake tester inserted in top cake layer comes out clean, about 30 minutes. Unmold cakes, and transfer them to a wire rack to cool. In a small bowl, whisk together confectioners' sugar and juice. Place rack over parchment paper; drizzle cakes with glaze.