Preheat the oven to 350°F (177°C) . Grease and line a 8x8 inch cake pan. Sift together the flour, baking soda, cocoa powder and salt. Set aside.
In a mixing bowl, add melted butter, oil and granulated sugar and beat on medium until lighter in color, about 2 minutes.
Add the eggs one at a time, mixing well after each addition (about 30 seconds). Scrape the sides of bowl to make sure everything is combined. Add vanilla extract and red food coloring. Mix to combine.
Reduce the speed to low, mix in the dry ingredients in 3 parts, alternating with buttermilk. Start and finish with the dry ingredients. Do not overmix.
Add the white vinegar and fold it in with a spatula.
Pour the batter in the cake pan. Use a spatula to even out the top. Bake in the preheated oven for about 20-25 minutes or until a toothpick inserted in the center comes out clean. Make sure you don't over bake it.
Let the cake cool completely before frosting.