Preheat your oven to 350°F.
Grease your loaf pan with butter.
Line it with parchment paper too.
This prevents the cake from sticking.
Take a medium bowl.
Add flour, baking powder, and salt.
Whisk them together well.
Set this bowl aside for now.
Put softened butter in a large bowl.
Add the granulated sugar to it.
Beat them together until fluffy.
This takes about 3 minutes.
Crack one egg into the mixture.
Beat it in completely.
Repeat with the remaining three eggs.
Mix well after each addition.
Pour in the key lime juice.
Add the lime zest and vanilla.
Mix everything together until combined.
Add half of the flour mixture.
Mix it in gently. Add the sour cream next.
Then add the remaining flour.
Don't overmix the batter.
Pour batter into your prepared pan.
Smooth the top with a spatula.
Bake for 60-70 minutes.
A toothpick should come out clean.
Mix powdered sugar and lime juice.
Add the lime zest too.
Stir until smooth and pourable.
Let the cake cool completely.
Remove it from the pan.
Pour glaze over the top.
Let it drip down the sides.