Step 1: Make the Blueberry Filling

• In a small saucepan, combine the blueberries, sugar, cornstarch, lemon juice, and vanilla extract.
• Cook over medium heat, stirring occasionally, until the mixture thickens (about 5–7 minutes).
• Remove from heat and set aside to cool. The filling will thicken further as it cools.

Step 2: Make the Cake

• Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
• In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
• Add the softened butter and beat on medium speed until the mixture resembles coarse crumbs.
• Add the buttermilk, eggs, and vanilla extract, and mix until just combined.
• Divide the batter evenly between the prepared cake pans and smooth the tops.
• Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cakes cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely.

Step 3: Make the Whipped Cream

• In a chilled mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until soft peaks form (about 3–5 minutes).
• Be careful not to overbeat, or the cream will turn into butter.

Step 4: Assemble the Cake

• Place one cake layer on a serving platter. Spoon half of the blueberry filling over the top.
• Add a layer of whipped cream on top of the blueberries.
• Place the second cake layer on top, then repeat with the remaining blueberry filling and whipped cream.
• Garnish with additional fresh blueberries and a light dusting of powdered sugar (optional).

Step 5: Serve

• Slice and serve immediately, or refrigerate for up to 4 hours before serving to allow the cake to set.