Preheat the oven to 350°F (180°C). Line a 12-cup muffin pan with cupcake liners.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, whisk together the granulated sugar, oil, eggs, sour cream, lemon juice, lemon zest, milk, and vanilla until smooth and well combined.

Add the dry ingredients to the wet ingredients and mix gently until just combined. Slowly stir in the milk until the batter is smooth. Do not overmix.

In a small bowl, toss the blueberries with 1 tablespoon flour. Gently fold them into the batter.

Divide the batter evenly between cupcake liners, filling each about ¾ full.

Bake for 16–18 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Add the blueberries, lemon juice, and granulated sugar to a small saucepan over medium heat. Cook, stirring occasionally, until the berries break down and the mixture thickens slightly, about 6–8 minutes.

Blend in a food processor until pureed, and let cool completely before using.

In a medium bowl with a hand mixer, beat the cream cheese and butter until smooth and creamy.

Add the powdered sugar gradually until combined.

Add the cooled blueberry puree, and vanilla extract. Beat until light and fluffy, about 2–3 minutes.

If the frosting is too soft, gradually add more powdered sugar until you reach your desired consistency, or refrigerate for 15–20 minutes before piping.

Frost fully cooled cupcakes. Garnish with fresh blueberries or lemon slices if desired.