1/2 pound (2 sticks) unsalted butter at room temperature
2 1/2 cups granulated sugar, divided
4 extra-large eggs, at room temperature
1/3 cup grated lemon zest lightly packed (6 to 8 large lemons - Use only fresh lemon juice and zest) 3 cups all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1 teaspoon kosher salt
3/4 cup freshly squeezed lemon juice
3/4 cup buttermilk, at room temperature
1 teaspoon pure vanilla extract
For the glaze:
2 cups confectioners' sugar
3 1/2 tablespoons freshly squeezed lemon juice
Preheat the oven to 350 degrees F. Grease and flour 2 (8 1/2 by 4 1/4 by 2 1/2-inch) loaf pans. Cream the butter and 2 cups granulated sugar in the bowl of an electric mixer fitted with the paddle attachment, the key to great cakes is beating the butter and sugar until the mixture's light and fluffy, about 5 minutes. With the mixer on medium speed add the eggs, 1 at a time, and the lemon zest.
Sift together the flour, to make sure there are no lumps, baking powder, baking soda, and salt in a bowl. Separately, combine 1/4 cup lemon juice, the buttermilk, and vanilla. Add the flour and buttermilk mixtures alternately, beginning and ending with the flour. Divide evenly between the pans, smooth the tops, and bake for 45 minutes to 1 hour, until a cake tester comes out clean.
Cook 1/2 cup granulated sugar with 1/2 cup lemon juice in a small saucepan and cook over low heat until the sugar dissolves. When the cakes are done, cool for 10 minutes, invert them onto a rack set over a tray and spoon the lemon syrup over the cakes. Allow the cakes to cool completely.
For the glaze, combine the confectioners' sugar and the lemon juice in a bowl, mixing with a wire whisk until smooth. Pour over the tops of the cakes and allow the glaze to drizzle down the sides.
To freeze these cakes, prepare them except the glaze. Wrap them well in plastic wrap and freeze. When you're ready to use, defrost and glaze.