Preheat your oven to 350°F (175°C). Prepare your mini loaf pan by greasing it or spraying it with non-stick spray.
In a large mixing bowl, cream the softened butter and sugar together until light and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the key lime juice and zest until well combined.
In a separate bowl, whisk together the flour, baking powder, and salt. With the mixer on low speed, gradually add the flour mixture to the butter mixture, alternating with the milk, starting and ending with the dry ingredients.
Pour the batter evenly into the mini loaf pans. Bake for 25 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for about 10 minutes before transferring them to a wire rack to cool completely.
While the cakes cool, prepare the glaze by combining powdered sugar, key lime juice, and zest in a bowl. Adjust the consistency by adding more lime juice or powdered sugar as needed.
Once the cakes are fully cooled, drizzle the glaze generously over the top or serve it on the side. For added decoration, top each loaf with a slice of key lime.