Adjust the oven rack to the center position, and preheat the oven to 350 degrees F.
Grease a 9 x 5-inch loaf pan with 1 tablespoon butter, and dust with 1 tablespoon cake flour, tapping out the excess.
Place the 1/2 pound butter and the lemon zest in a small saucepan set over low heat. Gently melt the butter, whisking constantly. Set aside. Combine the sugar, eggs, and lemon juice in the bowl of a standing mixer. Use the whip attachment to beat the mixture on medium speed for about 30 seconds. Reduce the speed to low, and in a slow and steady stream, pour the melted butter and lemon zest into the bowl. Sift the remaining 1 1/2 cups cake flour, the baking powder, and salt into a medium bowl. Add the sifted flour mixture in 3 parts to the wet ingredients in the bowl of the stand mixer. Be sure to scrape down the sides of the bowl to ensure an evenly blended batter. Mix the batter just until blended, add the sour cream, and mix to blend.
Pour the batter into the prepared loaf pan and bake for 15 minutes. Reduce the oven temperature to 325?F, and continue to bake the cake until the top is a deep golden brown and a toothpick inserted in the center comes out clean, 40 to 45 minutes, rotating the pan after 20 minutes of baking. Remove the cake from the oven and place on a wire rack to cool in the pan for 10 minutes. Remove the cake from the pan and continue to cool on the rack until just warm. Pour the glaze over the cake while just warm.
Makes one 9-inch loaf cake, 8 to 10 servings