Preheat oven to 350°F. Butter and flour two 9-inch cake pans and line each with parchment paper.

In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt until well combined.

In a stand mixer or large bowl, cream butter and sugar on medium-high speed for 3 to 4 minutes until light and fluffy.

Add eggs one at a time, beating well after each addition. Mix in vanilla, vinegar, and blue food coloring until evenly colored.

Alternately add flour mixture and buttermilk in three batches, beginning and ending with flour mixture. Mix on low speed just until combined.

Toss blueberries with 1 tablespoon flour to coat, then gently fold into batter using a spatula.

Divide batter evenly between prepared pans and bake for 30 to 40 minutes, until a toothpick inserted in center comes out with a few moist crumbs.

Cool cakes in pans for 15 minutes, then turn out onto wire racks to cool completely (about 1 hour) before frosting.

For frosting, beat cream cheese, butter, and blueberry preserves until smooth. Gradually add confectioners' sugar on low speed, then add vanilla.

Increase mixer speed to high and beat for 5 minutes until light and fluffy. Refrigerate for 30 minutes until firm enough to spread, then frost cooled cake layers.