Preheat oven to 350°F (177°C). Line 2 cupcake tins with paper liners and set aside.

In a large mixing bowl or stand mixer with the paddle attachment, beat butter, vanilla, sugar, and lemon zest on medium speed until light and fluffy (about 2 minutes).

Add eggs one at a time, mixing well after each addition.

Reduce mixer speed to low and beat in sour cream, followed by milk. Turn mixer off.

Add 3¼ cups cake flour, baking powder, baking soda, and salt. Toss the dry ingredients gently with a fork before folding them into the wet mixture. Mix with a spatula until just combined—do not overmix.

In a separate small bowl, toss blueberries with the remaining 2 tbsp of cake flour, then gently fold them into the batter.

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

Bake one tray at a time for 18–21 minutes, or until a toothpick inserted in the center comes out clean.

Let cupcakes cool completely on a wire rack before frosting.

In a stand mixer or large bowl with a hand mixer, beat the butter on medium speed until smooth.

Gradually add confectioners’ sugar (½ cup at a time) while mixing on low speed until incorporated.

Add salt, sour cream, and milk. Mix until smooth.

Pour in cooled white chocolate and beat until the frosting is light, fluffy, and creamy—about 1 minute on medium-high speed.

Adjust consistency as needed by adding a little milk (if too thick) or more powdered sugar (if too soft).

In a small saucepan, combine blueberries and lemon juice over medium heat.

Simmer for about 12 minutes, gently smashing the berries as they cook, until the sauce thickens and turns deep purple.

Strain through a fine mesh sieve to remove skins and seeds.

Cool completely before using.

Pipe or spread the white chocolate frosting over the cooled cupcakes.

Drizzle 1 tsp of blueberry sauce over each cupcake.

Top with a few fresh blueberries or white chocolate shavings if desired.