Heat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan, 9-inch springform pan, or 9-inch square pan, then line the bottom with parchment if desired.

Whisk the flour, baking powder, and salt together in a medium bowl. For especially well-distributed berries, reserve 1 tablespoon of the measured flour for tossing with the blueberries.

Beat the softened butter and granulated sugar for 2–3 minutes, until light and fluffy. Add the eggs one at a time, beating after each addition, then mix in the vanilla and lemon zest.

Add the dry ingredients in two or three additions, alternating with the milk. Mix only until the ingredients are combined; the batter will be fairly thick.

Toss the blueberries with 1 tablespoon of the measured flour, if using, and gently fold them into the batter. If using frozen blueberries, keep them frozen rather than thawing them.

Spread the batter evenly in the prepared pan. Bake for approximately 40–50 minutes, until the top is golden and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Cool the cake in the pan for 10–15 minutes, then transfer it to a wire rack. Allow it to cool completely before glazing.

Whisk the confectioners’ sugar and lemon juice until smooth, adding the optional lemon zest if desired. Drizzle the glaze over the fully cooled cake and let it settle before slicing.