1 Preheat oven to 350 degrees F. Lightly grease and flour a 8 1/2 x 4 1/2 x 2 1/2 loaf pan.
2 Make the sour milk. In a small bowl, add 1/3 cup milk and 2 tablespoons of lemon juice, stir to combine. Let sit about 10 minutes.
3 Mix the dry ingredients. In a medium bowl, stir together the flour, baking powder, baking soda, and salt.
4 Cream the butter and sugar. In a large bowl, beat the butter with an electric mixer on medium speed for about 10 seconds, or until smooth. Beat in the granulated sugar until well blended and light and fluffy, about 2 minutes. Beat in the eggs, one at a time, beating after each egg is added. Beat in the vanilla and lemon zest.
5 Combine all ingredients. Alternate adding the flour mixture and the milk mixture to the butter mixture, beating on low after each addition, until the batter is just combined.
6 Bake the cake. Pour the cake batter into the prepared pan. Bake for 45-60 minutes, or until toothpick inserted into the middle comes out clean. Cool slightly, then remove the cake from the pan to finish cooling on a wire rack.
7 Make the glaze, In a medium bowl, whisk together the powdered sugar, 2 teaspoons lemon juice, and 1 tablespoon of milk. Whisk in more milk as needed until thick but spreadable. Spoon the glaze over the top of the cake, so it can drizzle down the sides.