01 - Preheat oven to 350°F. Lightly grease a 9x13-inch sheet pan and line with parchment paper.
02 - In a medium mixing bowl, whisk together the flour, baking powder, baking soda, and salt until evenly incorporated.
03 - In a large bowl, beat the softened butter with granulated sugar using an electric mixer until the mixture is light and airy. Sequentially add the eggs, beating well after each addition.
04 - Stir in lemon zest, fresh lemon juice, and vanilla extract until fully blended.
05 - Alternately add the flour mixture and sour cream to the wet ingredients, beginning and ending with the flour. Mix on low speed to avoid overworking the batter.
06 - Pour in lemon-lime soda and gently fold until just combined. Take care not to overmix.
07 - Evenly spread the batter into the prepared pan and bake in the center of the oven for 22–25 minutes, or until a toothpick inserted into the center emerges clean.
08 - Allow cake to cool completely in the pan before adding the glaze.
09 - In a separate bowl, whisk together powdered sugar, lemon juice, lemon zest, and lemon-lime soda until smooth and pourable.
10 - Pour the glaze over the cooled cake, spread evenly, and let set until firm to the touch.
11 - Cut into 16 uniform squares and present for serving.