Preheat oven to 325°. Spray a 13x9-inch baking pan with baking spray with flour. Line with parchment paper.
In a large bowl, whisk together melted butter and sugars until combined. Whisk in Lemony Sweet Tea Concentrate, eggs, buttermilk, ¼ cup water, and vanilla until well combined.
In a medium bowl, whisk together flour, baking powder, salt, and baking soda. Stir flour mixture into butter mixture until just combined. Spread batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, 35 to 40 minutes. Let cool completely in pan on a wire rack. Remove from pan and place on a serving platter.
Top with Creamy Lemonade Frosting. Garnish with lemon slices and zest, if desired. Serve immediately.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/sweet-tea-lemonade-cake/