Preheat your oven to 350°F (176°C) and line a cupcake pan with liners.

Cream together 6 tablespoons of room temperature unsalted butter and 3/4 cup sugar using an electric mixer on medium speed for about 3-4 minutes.

Add 6 tablespoons of sour cream, 1/2 teaspoon of vanilla extract, and 1 tablespoon of lemon zest to the creamed mixture and mix on low speed.

Gradually add in 3 large egg whites, mixing well after each addition.

Sift together 1 1/4 cups of all-purpose flour, 2 teaspoons baking powder, and 1/4 teaspoon salt.

Combine 1/4 cup milk, 1 tablespoon water, and 3 tablespoons of fresh lemon juice in a small measuring cup.

Add half of the dry ingredients to the wet mixture, then the milk mixture, followed by the remaining dry ingredients, mixing gently.

Fill each cupcake liner about 3/4 full with batter and bake for 15-17 minutes.

Allow the cupcakes to cool in the pan for about 2-3 minutes before transferring them to a cooling rack.

Beat together 1/2 cup salted butter and 1/2 cup shortening until smooth and creamy.

Gradually mix in 4 cups of sifted powdered sugar until combined.

Add in 1 1/4 teaspoons of lavender extract and a splash of milk or water if needed.

Pipe the creamy lavender frosting generously onto the cooled cupcakes and decorate with edible lavender flowers and half lemon slices.