Begin by warming 1 cup of whole milk in a saucepan. Stir in 2 tablespoons of dried culinary lavender and let steep for 20 minutes.

In a saucepan, combine 1 cup of sugar with 1 cup of water and bring to a boil. Stir in the lavender milk and simmer for 10 minutes.

Preheat your oven to 350°F (175°C). Grease three 8-inch round cake pans with butter and line with parchment paper.

Combine the cooled lavender milk with 1 cup of sour cream in a mixing bowl. In another bowl, mix together 2 cups of cake flour, 1.5 teaspoons of baking powder, and a pinch of salt. Gradually combine both mixtures and add ½ cup of butter and 1 teaspoon of vanilla extract.

Divide the batter among the cake pans. Bake for 20-22 minutes, or until a toothpick comes out clean. Cool in pans for 10 minutes, then transfer to wire racks.

Beat together ½ cup of butter and 8 ounces of cream cheese until smooth. Gradually add 4 cups of confectioners’ sugar, mixing on low, then add vanilla extract and milk.

Soak each cooled cake layer in lavender syrup. Spread frosting and blackberry jam between layers. Finish with a crumb coat and chill, then frost completely and garnish with fresh blackberries.