Preheat oven to 350°F (175°C). Generously grease a 9-inch round cake pan.
Whisk together the flour, baking powder, and salt. Set aside.
Using an electric mixer on medium speed, beat the butter, sugar, and brown sugar until creamy. Add the egg and vanilla, mixing well.
Add the flour mixture in 3 portions, alternating with the milk. Mix just until combined.
Transfer the batter to prepared pan. Scatter the blueberries over the top of the batter and lightly press them into the batter. Sprinkle the top with sanding sugar.
Bake for 10 minutes. Reduce oven temperature to 325°F (160°C). Bake for 50-60 minutes, or until the cake is golden brown and firm.
Cool in the pan for 15 minutes. Run a knife around the edges of the cake. Transfer the cake to wire rack to cool completely. (You'll need to flip the cake twice so it can cool right side up.)
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Notes
Recipe slightly adapted from Martha Stewart.
To store. This cake will keep at room temperature for 3-4 days. Wrap it well, or transfer smaller portions of leftovers to an airtight container.
To freeze. You can freeze blueberry cake for up to 3 months. Wrap it well or freeze it in an airtight storage container; let it thaw at room temperature before serving.