Preheat oven to 350F; butter and flour a 9-inch cake pan.
In a large bowl, whisk together the maple syrup, canola oil, eggs, and ginger.
In a medium bowl, whisk together the almond flour, all-purpose flour, cinnamon, baking soda, and salt.
Gradually stir the dry ingredients into wet, then fold in parsnips.
Pour into the prepared cake pan and bake about 38 minutes, until a toothpick inserted in the center comes out clean.
Cool completely before frosting.
For the Buttercream:
In a double boiler, whisk together the egg whites and maple syrup. Heat until the sugar is dissolved and the mixture is warm (about 140F), whisking frequently, about 3 to 5 minutes.
Transfer the egg white mixture to the bowl of a stand mixer fitted with the whisk attachment and beat on high speed until the mixture is thick and glossy, about 5 to 7 minutes.
Add the vanilla bean paste, salt, and cinnamon, then beat in the powdered sugar.
Add the butter and cream cheese piece by piece while beating; stop beating when the buttercream is thick and smooth.
Once the cake is cooled, frost it with the buttercream and decorate the top with sliced almonds if desired.
Notes
Adapted from Michel Richard’s recipe for Maple Parsnip Cake with Maple Meringue Frosting in Sweet Magic.