Preheat & Prepare: Preheat your oven to 350°F (175°C) and grease a 9-inch round baking pan.
Beat Butter & Sugar: In a large mixing bowl, beat the softened unsalted butter and granulated sugar together until the mixture is light and fluffy.
Add Eggs: Add the eggs one at a time, beating well after each addition until smooth.
Combine Dry & Wet Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt. Slowly incorporate the dry mixture into the wet ingredients, mixing until just combined to avoid a dense texture.
Add Flavor: Stir in the fresh key lime juice, key lime zest, and fold in the sour cream until evenly spread throughout the batter.
Bake: Transfer the batter to the prepared baking pan and spread it evenly on top. Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Cooling: Allow the cake to cool in the pan for 10 minutes before turning it out onto a wire rack to cool completely.
