This small blueberry cake is tender, moist, and dotted with fresh blueberries. It's a small batch dessert, enough for one or two, with no full cake left over.
Preheat the oven to 350°F (177°C) and butter a 5×5-inch baking dish. Set the dish on a rimmed baking sheet.
In a medium bowl, beat the butter and sugar with an electric mixer on medium speed until pale and creamy, about 2 minutes.
Beat in the egg, lemon juice, and vanilla until the mixture is smooth.
In a separate bowl, whisk together the flour, baking powder, and salt.
Add the dry ingredients to the butter mixture and mix on low just until combined.
Pour in the milk and stir until the batter is smooth.
Gently fold in the blueberries with a rubber spatula, just until they're spread evenly through the batter.
Spoon the batter into the prepared dish and smooth the top.
Bake for 40 to 45 minutes, until the top is golden and a toothpick inserted in the center comes out clean.
Let the cake cool, then dust with powdered sugar if you like.
Notes
Use a 5×5-inch baking dish. This cake is sized for a 5×5-inch dish, and the bake time matches it. A larger dish spreads the batter thin and bakes faster, while a smaller, deeper one takes longer.Soften the butter all the way. Soft butter is what lets you cream in the air that lifts this cake. Leave it at room temperature until your finger leaves a dent without the butter losing its shape. Cold butter won't whip up the same way.Check that your baking powder is fresh. Only ⅛ teaspoon does the lifting here, so stale baking powder shows up fast as a flat cake. To test it, stir ¼ teaspoon into ½ cup of hot water. If it bubbles right away, it's still good.Spoon and level the flour. With only ¾ cup of flour, scooping straight from the bag packs in too much and dries out the cake. Spoon it into the dry measuring cup and level the top with a knife.Mix just until combined. Once the flour goes in, stir only until it disappears. Overmixing works the gluten and makes the crumb tough, so stop while the batter still looks a little rough.Start checking at 40 minutes. Ovens run differently, so begin checking at the 40-minute mark. The cake is done when the top is golden and a toothpick in the center comes out clean.If doubling the recipe, bake in either two 5x5-inch baking dishes or one 6x8-inch baking dish.