Preheat oven to 350°F. Spray a 9x5” loaf pan (I used a 9x4” loaf pan) with baking spray and line with parchment, leaving an overhang so the cake can be easily lifted from the pan once baked and cooled.
In a large bowl, cream butter and sugar on medium speed with an electric mixer until lighter in color and fluffy. Add vanilla, butter flavoring, and egg. Mix well.
Add flour, baking powder, salt, and milk. Mix until all dry ingredients are incorporated. Set aside.
To make the red velvet cake batter:
In another large bowl, cream butter and sugar on medium speed with an electric mixer until lighter in color and fluffy. Add vanilla and egg; mix well.
Add flour, cocoa powder, baking powder, salt, and milk. Mix until all dry ingredients are incorporated.
Stir in red food coloring. Feel free to add a little more if you’d like a more vibrant color!
Spoon half of the butter cake batter into the prepared pan and smooth with a rubber spatula. Spoon half of red velvet batter on top of that. Repeat with the second half of the butter and red velvet cake batters.
To help create a swirled and marbled look, run a knife through the center of the batter, using and up and down motion. Repeat on the left side, closer to the edge of the pan, and then the same on the right side.
Bake for 50 to 55 minutes, or until set in the center and a toothpick inserted into the center comes out clean. (A couple of crumbs are okay.)
Transfer to a wire rack to cool completely.
To make the vanilla bean cream cheese frosting:
Mix cream cheese and vanilla bean paste until smooth. Add half of powdered sugar; mix well. Repeat with second half of powdered sugar. Spread on top of the cooled loaf cake, creating large swoops in the frosting.
Cut into slices to serve. Store covered at room temperature.