Preheat the oven to 350 degrees F. Butter and flour 2 (9-inch) cake pans and line each pan with a round of parchment paper.
Whisk together the flour, cocoa powder, baking soda and salt in a small bowl
Cream the butter, sugar and oil in a stand mixer fitted with the paddle attachment until light and fluffy. Add the eggs, one at a time, scraping down the sides of the bowl and beat until incorporated. Beat in the vanilla, vinegar and food coloring.
Add the flour mixture to the batter in 3 batches alternating with the buttermilk, mixing well after each addition. Divide the batter evenly between the prepared pans and bake for 30 to 40 minutes or until a wooden skewer inserted into the center comes out with a few moist crumbs. Cool on a baking rack for 15 minutes before removing the cake from the pans. Let cool completely before frosting. Slice each cake into 2 layers and frost.
Combine the cream, milk, vanilla bean and seeds in a small saucepan and bring to a simmer over medium-high heat. Remove the vanilla bean and discard. Add the flour and cook, whisking constantly, until thickened to a paste, about 2 minutes. Scrape into a bowl, cover and refrigerate until very cold, at least 2 hours.
Combine the butter and sugar in the bowl of a stand mixer fitted with the whisk attachment and beat until the mixture is very fluffy and the sugar is totally dissolved, about 6 minutes. Add the cold paste, a few tablespoons at a time to the butter mixture and whip until light and fluffy.