Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line with baking parchment.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Then, mix in the buttermilk.
In another bowl, sift together the flour, baking powder, baking soda, salt, and dried lavender.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix.
Gently fold in the fresh blueberries.
Divide the batter evenly between the two prepared cake pans.
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then invert onto a cooling rack to cool completely.
While the cakes are cooling, prepare the lavender buttercream. In a mixing bowl, beat the softened butter until creamy.
Gradually add powdered sugar, mixing well. Pour in the heavy cream, vanilla extract, and a pinch of salt. Mix until smooth and fluffy.
Add in the dried lavender and mix to combine.
Once the cakes have cooled completely, place one layer on a serving plate and generously spread half of the buttercream over the top.
Place the second cake layer on top and frost the top and sides of the cake with the remaining buttercream.
Optionally, decorate with extra blueberries and lavender sprigs for presentation.
Slice, serve, and enjoy!