Preheat your oven to 350°F and grease a 9x13-inch baking pan. In a large bowl, cream together the softened butter and granulated sugar until it's light and fluffy—this takes about 2 minutes of beating. Add the eggs one at a time, mixing well after each addition.

Whisk together the flour, baking powder, salt, and vanilla powder in a separate bowl. Alternate adding the dry ingredients and milk to the butter mixture, starting and ending with dry ingredients. Gently fold in the fresh blueberries so they're evenly distributed throughout the batter.

Pour the batter into your prepared pan and spread it evenly. Bake for 30-35 minutes until a toothpick inserted in the center comes out mostly clean (a few crumbs are totally fine). Don't overbake or the cake gets dry—mine always pulls out right at the 32-minute mark.

While the cake bakes, whisk together the powdered sugar, lemon juice, and lemon zest in a small bowl. This creates your glaze that'll soak into all those poke holes. The mixture should be pourable but still slightly thick.

Remove the hot cake from the oven and let it cool for exactly 5 minutes on the counter. This timing's crucial—if you poke it too hot, the holes'll be too big and loose. If it's too cold, the glaze won't absorb properly.

Using a fork or wooden skewer, poke holes all over the cake's surface, spacing them about 1 inch apart. I usually go in rows to keep things organized, but honestly any pattern works. You're aiming for 40-50 holes total so the glaze has plenty of spots to sink in.

Pour the lemon glaze slowly over the entire cake, letting it drip into all those poke holes. You'll see it absorb as you pour—it's pretty satisfying to watch. Let the cake cool completely at room temperature before serving (about 2 hours).