Position a rack in the center of your oven and preheat to 350°F/176°C. Grease a standard 9×5 inch loaf pan with oil and line the bottom and sides of the pan with two pieces of parchment paper cut to fit.
Sift together the all-purpose flour, spelt flour, cornstarch baking soda, pumpkin spice, and salt in a medium bowl and mix well to combine the ingredients. It is important to sift the dry ingredients and combine them well before adding to the wet ingredients. For why, check out the “tips for baking this healthy vegan pumpkin cake” section.
Pour 1/2 cup liquid from a can of chickpeas (aquafaba) into a small bowl. With an electric mixer, beat the aquafaba on medium speed until it starts to get foamy, 60-90 seconds.
In a large bowl, add the pumpkin purée, almond butter, coconut sugar, maple syrup, and almond milk. Beat the wet ingredients with the mixer until smooth and very well-combined. Beat in the whipped aquafaba and vanilla to incorporate and until well-combined.
Place a mesh strainer over the bowl with the liquid ingredients and sift in the dry ingredients. Fold the dry ingredients into the wet using a wooden spoon or whisk, taking care to not overmix.
Pour the batter into the prepared loaf pan and bake for 35 minutes. Then tent the loaf with a piece of aluminum foil to ensure even cooking and prevent premature browning. Continue baking for another 20-30 minutes (total of 55-65 minutes), or until a toothpick inserted near the center comes out mostly clean, with just a few crumbs. If the loaf is browning unevenly, you can move it to a lower rack. I recommend checking at 50 or 55 minutes, just to be sure.1. NOTE: If your loaf pan is an 8×4-inch pan (instead of the standard 9×5-inch pan), your loaf will be even thicker due to the smaller pan size, so you might need to bake the loaf a bit longer, closer to 70 minutes.
Transfer the pumpkin bread to a wire rack to cool. Wait until it is completely cooled (at least 45 minutes, ideally an hour) before slicing. If you cut it too early, the loaf might be a bit underbaked in texture.
If you made the Cashew Buttercream Frosting, wait until the loaf is cooled to frost it. You can leave the frosted loaf out on the counter for a few hours, but it should be covered and refrigerated after that. If you do not frost the loaf, wrap it tightly in plastic wrap and store at room temperature (the plastic wrap ensures it stays moist).