Heat oven to 350F. Thoroughly butter and flour a 12-cavity mini Bundt pan, tapping out excess. Whisk together flour, baking powder, and salt in a medium bowl.

Beat butter and sugar on medium-high speed until pale and fluffy, about 3 minutes. Add eggs one at a time, beating well after each. Mix in lemon zest, lemon juice, and vanilla. Reduce speed to low and add flour mixture in three additions, alternating with milk in two additions, beginning and ending with flour. Mix just until combined.

Divide batter evenly among prepared cavities, filling each about three-quarters full. Smooth tops with a small offset spatula. Bake until cakes spring back when lightly pressed and a toothpick comes out clean, 16 to 18 minutes. Cool in pan 10 minutes, then invert onto a wire rack to cool completely.

Whisk powdered sugar and lemon juice until smooth and pourable but thick enough to coat. Add more lemon juice by the teaspoon if too thick, or more sugar if too thin.

Spoon glaze over cooled cakes, letting it drip down the sides. Sprinkle with lemon zest while glaze is still wet. Let set at room temperature at least 15 minutes before serving.