Start by preheating your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan. You want the cake to slide out easily once it's baked.

Take a bowl and toss your fresh blueberries with a tablespoon of flour. This helps prevent them from sinking to the bottom of the cake during baking. Set this bowl aside for now.

In a large mixing bowl, cream together the softened butter and granulated sugar. Use a handheld mixer or stand mixer for this task. You should be aiming for a light and fluffy mixture, about 3-4 minutes. This adds air, giving your cake a beautiful texture.

Next, add the egg, vanilla extract, and lemon juice to the creamed mixture. Beat until well combined. The mixture should now look smooth and shiny.

In another bowl, whisk together your flour, baking powder, cinnamon, and salt. This ensures even distribution of the leavening agent and spices.

Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Start and end with the flour mixture. Mix until just combined. You don’t want to overmix, or your cake could turn out dense.

Gently fold in your blueberry mixture. You want the blueberries evenly distributed without breaking them apart.

Pour the cake batter into your prepared pan and spread it evenly. Bake for 45-50 minutes or until a toothpick inserted into the center comes out clean. You can also lightly press the top of the cake; if it springs back, it's ready.

Let the cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely. Serve warm or at room temperature, cut into generous slices.