Preheat the oven to 350ºF and prepare your cake pan(s). You can use two 6-inch pans or one 8-inch round or square pan. Spray the pan(s) lightly with oil, then line the bottom with parchment paper for easy cake removal later.: As the oven warms, you will notice the kitchen gradually taking on a faint warmth and you may smell a hint of dry heat when the racks start to glow. Proper preheating ensures the cake begins rising immediately when placed inside, which helps build an even crumb and prevents an overly dense center. I line the bottom with parchment and lightly oil the sides, which promotes an easy release and keeps the exterior from tearing when you remove the cake. A common mistake is opening the oven door to check too often, which can cause uneven rise, so resist peeking for at least the first half of the bake time.
In a large bowl, combine the almond flour, potato starch, tapioca starch, cacao powder, baking powder, and salt. Use a whisk to stir well and break up any clumps.: When you whisk these dry ingredients, you should see a uniform, powdery mixture with a deep, chocolatey hue. Whisking breaks up clumps and aerates the mixture slightly, aiding lift and consistent texture. I like to sift or vigorously whisk the cacao because it can clump, and those dry lumps would create pockets of intense flavor or dry bits in the finished cake. Avoid using a mixer at this stage, over agitation can warm the fat components later when combined, affecting final texture.
To the dry ingredients, add in the water, coconut oil, maple syrup, and vanilla. Whisk again, until the batter is smooth. Pour the batter into the prepared cake pans, dividing it evenly if using the two 6-inch pans.: As the liquids join the dry mix, smell the first bright notes of maple and a subtle coconut sweetness, and watch the batter transform into a glossy, smooth ribbon when you lift your whisk. This viscosity is the right sign that the starches have hydrated and the fats have evenly distributed. Whisk until smooth with no visible streaks of dry powder, scraping the bowl to ensure uniformity. A troubleshooting tip: if the batter looks overly thin, check your measures; too much liquid will make the cake overly flat and require a longer bake.
Bake at 350ºF until the cake has fully risen in the center, and is slightly cracked around the edges. This takes about 35 minutes for the two 6-inch cake pans, and 40 to 45 minutes in the 8-inch cake pan. (If using a glass or ceramic baking dish, it might even take a little longer.): Pouring should feel effortless as the batter flows with a satin sheen. Even division ensures uniform baking and consistent rise for layered assembly or serving. Tap the pans gently on the counter once to release air bubbles and to settle the batter, watching small bubbles rise and disappear. The main mistake here is uneven distribution, which causes one layer to cook faster and potentially overbrown; I use a kitchen scale or eyeball equal portions by sight to avoid that.
Allow the cake to cool completely before removing from the pan and frosting. This cake will keep well when tightly covered on the counter for up to 24 hours, but for the best shelf life you can store it in an airtight container in the fridge for up to a week.: During baking you will notice a deep chocolate scent intensifying and a slight crackle at the pan edges as the top sets. For two 6 inch pans expect around 35 minutes, whereas an 8 inch may take 40 to 45 minutes, and glass dishes often need more time because they retain heat. The correct doneness shows a firm center that springs back gently, and a toothpick inserted near the center comes out with a few moist crumbs. Avoid overbaking which dries the crumb; if the edges brown quickly but the center is still unset, lower the oven heat by 10 to 15 degrees and continue to monitor.
Allow the cake to cool completely before removing from the pan and frosting: Cooling is when the crumb finishes setting and the crumb firms enough to slice cleanly. You will feel residual warmth still in the pans, and the aroma becomes steadier, not as sharp as in the hot bake. If you try to unmold while warm, the cake can break or compress, so patience matters. A common mistake is frosting while warm, which causes frosting to melt and slide; wait until the cake is at room temperature before applying any frosting or fillings.