Preheat the oven to 350°F. Grease a 9-inch round cake pan and line it with parchment for easy removal.
In a small bowl, whisk together almond flour, arrowroot powder, baking soda, baking powder, and salt until evenly combined.
In a larger bowl, whisk the melted butter and sugar for about 30 seconds. Add the eggs, milk, and vanilla extract, whisking until smooth and creamy.
Using a spatula, gently fold the dry mixture into the wet ingredients just until no streaks remain. Avoid over mixing.
Pour the batter into the prepared pan and spread evenly. Bake for 20–25 minutes, until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Let the cake cool in the pan for 20 minutes before transferring to a wire rack to finish cooling for another 40 or so minutes. Top with whipped cream or frosting if desired.