Preheat oven to 180ºC (360°F) and fold a 20 cm (7.8 inches) cake mold with parchment paper.
In a large mixing bowl, combine all dry ingredients: flour, almond flour, brown sugar, cocoa powder, baking powder and a pinch of salt. Give it a quick stir to mix the powders.
Using a spatula or fork, make a hole in the center of the dry ingredients. Pour in milk, vegetable oil, orange juice (optional), apple cider vinegar and vanilla extract. Start mixing gently, until you get a smooth cake batter without lumps.
Transfer eggless cake batter to the prepared mold, then bake in hot oven for about 30 minutes. The cake is ready when a toothpick inserted into its center comes out clean. Remove from the oven and let cool completely before serving.