Preheat oven to 350°F. Cream the 3/4 cup butter and 3/4 cup sugar until pale and fluffy, about 3 minutes. Add the 2 eggs one at a time, then mix in the lemon zest, 2 tablespoons lemon juice, and vanilla.

In a separate bowl, whisk the 1 1/2 cups flour, baking powder, and salt for 30 seconds.

On low speed, add the flour mixture in three parts alternating with the 1/2 cup sour cream, starting and ending with flour. Toss the 1 cup blueberries with the 1 tablespoon flour, then fold them in gently.

Pour the batter into a parchment-lined 9x5-inch loaf pan. Bake 55 to 65 minutes until a toothpick comes out with a few moist crumbs. Cool in the pan 10 minutes, then cool completely on a rack.

Whisk the 1 cup powdered sugar with 2 tablespoons lemon juice, adding more juice until thick but pourable. Drizzle over the cooled cake. Let the glaze set 15 minutes before slicing.