In a large mixing bowl, whisk together the 2 cups all-purpose flour, 3/4 cup granulated sugar, 2 tsp baking powder, and 1/2 tsp fine salt until evenly distributed and aerated.

Mix wet ingredients

In a separate bowl or large measuring cup, whisk together the 2 large eggs, 1 cup whole milk, 1/2 cup melted unsalted butter (cooled slightly), and 2 tsp vanilla extract until smooth.

Combine wet and dry

Make a well in the center of the dry ingredients and pour in the wet mixture. Stir gently with a spatula or wooden spoon until just combined—no large streaks of flour remain. Do not overmix; a few small lumps are fine.

Add-ins & Topping

Fold in blueberries and lemon zest

Gently fold 1 cup blueberries and 1 tbsp lemon zest (if using) into the batter, distributing them evenly without crushing the berries. If using frozen blueberries, fold them in straight from frozen to minimize color bleed.

Transfer to pan and top

Scrape the batter into the prepared pan and spread into an even layer. Sprinkle the top evenly with 1 tablespoon turbinado or coarse sugar for a crunchy, caramelized finish.

Bake

Bake in the preheated oven for 30–38 minutes, or until the top is golden and a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). Rotate the pan halfway through baking for even browning if your oven has hot spots.

Cool and serve

Allow the baked cake to cool in the pan on a wire rack for 15–20 minutes. Use the parchment overhang (or run a knife around the edges) to lift the cake from the pan and finish cooling on the rack. Serve warm or at room temperature, cut into 9 squares.