Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, and salt until well combined.
In another bowl, mix the buttermilk, vegetable oil, eggs, and vanilla extract until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Be careful not to overmix.
Gently fold in the fresh blueberries until evenly distributed throughout the batter.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then transfer them to wire racks to cool completely.
While the cakes are cooling, prepare the whipped cream by beating the heavy cream, powdered sugar, and vanilla extract in a mixing bowl until soft peaks form.
Once the cakes are completely cool, place one layer on a serving plate. Spread a layer of whipped cream on top, then place the second cake layer on top.
Frost the top and sides of the cake with the remaining whipped cream and garnish with fresh blueberries.