In a bowl mix sour cream, buttermilk, and lemon juice. To the butter mixture add ⅓ of the dry ingredients, mixing until just combined, then ½ of the wet ingredients, then repeat with the remaining ingredients ending with the flour mixture.
In a small pot over low-medium heat combine lemon juice and granulated sugar for 5 minutes, constantly whisking. Pour over just baked cake, I use a pastry brush to get every nook and cranny of the cake. Let cool completely