1. Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan (line with parchment if you want easy lifting).

2. In a large bowl, cream the butter and sugar until pale and fluffy, about 2–3 minutes.

3. Add the eggs one at a time, mixing well after each addition. Mix in the vanilla, lemon zest, and lemon juice.

4. In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.

5. Add the dry ingredients to the wet ingredients in 2–3 additions, alternating with the buttermilk. Mix just until combined (don’t overmix).

6. Gently fold in the blueberries.

7. Spread the batter evenly into the prepared pan and smooth the top.

8. Bake 35–45 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

9. Cool in the pan before dusting with powdered sugar (optional), then slice and serve.