Medium Recipe

Preheat and prepare

Preheat the oven to 350°F (175°C). Lightly grease or line a medium (about 8-inch) round or square baking dish or a muffin tin for individual portions.

Combine dry ingredients

In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until evenly combined.

Mix wet ingredients

In a separate bowl, whisk the melted butter, egg, milk, and vanilla extract until smooth and homogenous.

Make the batter

Pour the wet mixture into the dry ingredients and stir gently until just combined. Do not overmix; a few small lumps are fine. If batter seems too thick, add up to 1-2 tablespoons of additional milk to reach a medium cake-batter consistency.

Add fillings

Fold the blueberries and lemon zest into the batter gently, reserving a few berries for the top.

Assemble

Spoon the batter into the prepared medium baking dish or divide among muffin cups. Smooth the top with a spatula and press the reserved blueberries lightly into the surface. Sprinkle the brown sugar evenly over the top and, if using, a little coarse sugar for crunch.

Bake

Bake in the preheated oven for 20-30 minutes for an 8-inch dish or 16-20 minutes for muffins, until the top is golden, a toothpick inserted into the center comes out clean or with a few moist crumbs, and the internal temperature registers about 205°F (96°C) if using an instant-read thermometer.

Cool and serve

Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool slightly before slicing or serving. Serve warm or at room temperature.