Preheat oven to 325F. Grease a 9x5 inch loaf pan and line the bottom and sides with overhanging parchment paper.
In a medium-sized bowl, whisk together the almond flour, cornstarch, baking powder and salt.
In a large mixing bowl, use a handheld or stand mixer on medium high speed to beat together the eggs and sugar until foamy, about 1 minute.
Add the oil, milk and vanilla and mix until just combined.
Add the dry ingredients to the wet mixture and mix again until just combined.
Transfer a little less than half of the batter to a separate bowl. Add the cocoa powder, 2 tablespoons of milk and 1 tablespoon of oil. Mix until just combined.
Use an ice cream scoop to layer portions of the batter into the prepared loaf pan, alternating between the vanilla and chocolate batters. Once done, use a knife to swirl the batters around. (Just up and done the pan a few times should do it).
Bake for 39-42 minutes, or until a toothpick inserted into the middle comes out clean. Let cool in the pan for 10-15 minutes before using the sides of the parchment paper to lift the loaf out of the pan and transfer to a wire rack to cool completely.
Notes
Use a lighter colored loaf pan and line it with parchment paper. This will help prevent the bottom and sides from browning too much.
Room temperature ingredients. This is especially important for the eggs. At room temperature, they will beat together with the sugar easily and help it dissolve quickly. I also store my almond flour in the fridge, so I let it come to room temperature before I get started.
Be careful not to overbake. Even though we're baking this loaf on a lower temperature, ovens differ and almond flour browns quickly. Keep an eye on the loaf as it approaches the 40 minute mark and test for doneness with a toothpick.
Optional ganache topping. Chop up 4 ounces of dark chocolate and place in a glass bowl. Heat ¼ cup of heavy cream (on the stove top or in the microwave). Pour over the chopped chocolate, cover and let sit for a few minutes. Stir until all of the chocolate is melted. Pour over top of the cooled loaf and place in the fridge for 10 minutes to set.