Preheat the oven to 350 F. Grease or line a 9×5-inch loaf pan with a piece of parchment paper.
In a small bowl whisk together the flour, baking powder, and salt.
In a large bowl cream together the butter and sugar until light and fluffy. Add in the eggs, vanilla extract, lemon zest, 1 tablespoon of lemon juice, and sour cream and mix until well combined.
Add the flour mixture to the wet ingredients and mix until just combined.
Pour the batter into the prepared pan and bake for 45-60 minutes, until a toothpick inserted into the center of the cake comes out clean. Let the cake cool completely.
In a small bowl whisk together the confectioners' sugar and the remaining 3 tablespoons of lemon juice until smooth.
Pour the glaze over the cooled pound cake. Let the glaze set, then cut and serve.