Preheat your oven to 350°F (175°C) and lightly grease a 9x5 loaf pan to ensure easy release.

In a large mixing bowl, combine the softened unsalted butter and sugar. Beat until light and fluffy, about 2-3 minutes.

Gently beat in the eggs one at a time, then add the key lime zest, key lime juice, and vanilla extract.

In a separate bowl, whisk together all-purpose flour, baking powder, salt, and buttermilk until just combined.

Gradually pour the dry ingredients into the wet mixture, folding gently until just moistened.

Transfer the batter to the prepared loaf pan and bake for approximately 45 minutes, until a toothpick comes out clean.

While the bread is baking, whisk together powdered sugar and key lime juice until smooth for the glaze.

Cool the bread in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.

Drizzle the glaze over the warm bread and allow to set slightly before slicing.