01 - Preheat the oven to 350°F. Line an 8-inch round or square baking pan with parchment paper, or grease lightly with cooking spray.
02 - Place the old-fashioned rolled oats in a blender or food processor. Pulse until they reach a coarse, flour-like texture.
03 - In a medium mixing bowl, whisk together the oat flour, baking powder, baking soda, ground cinnamon, ground nutmeg, and fine sea salt until well blended.
04 - In a separate large bowl, whisk the eggs, maple syrup (or honey), melted coconut oil (or butter), and pure vanilla extract until smooth and combined.
05 - Add the dry ingredient mixture to the wet ingredients. Stir gently with a spatula or wooden spoon until just combined, being careful not to overmix.
06 - Gently fold in the grated carrots, raisins, and chopped nuts (if using) until evenly distributed throughout the batter.
07 - Pour the batter into the prepared baking pan. Use a spatula to spread the batter evenly and smooth the top.
08 - Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs. The edges should be lightly golden.
09 - Allow the cake to cool completely in the pan before slicing. Once cooled, cut into 8 equal slices and serve. Optional: top with cream cheese frosting or Greek yogurt.