Preheat oven to 350F.
Spray, or grease and flour a bundt cake pan.
Add the all purpose flour, the baking powder and the salt to a large bowl, and whisk to combine – set aside.
Mix the butter and the sugar in a large bowl, using a hand mixer until it looks sandy. Then add in the eggs, one at a time, mixing until combined between each addition (a few minutes on medium speed).
Alternate adding flour mixture and the milk, beginning and ending with flour (3 additions of flour and 2 of milk), fully incorporating after each addition.
With a spatula, scrape the sides of the bowl and give it a stir. Then, add in the key lime juice and zest and stir to combine.
Pour the batter into the greased bundt pan, and bake until a cake tester/toothpick inserted to the middle comes out lightly crumbly to clean (about 35-40 mins)
Move the cake pan to a cooling rack and let it cool for about 5-10 mins, then remove the cake from the pan and let it cool on the rack