Step 1

Make the carrot cake: Arrange a rack in the middle of the oven and heat to 350°F. Lightly coat a 9-inch springform pan with butter; set aside.

Step 2

Place the flour and baking powder in a large bowl and whisk to combine. Add the almond flour and whisk again; set aside.

Step 3

Place the sugar and egg yolks in a large bowl. Beat with an electric hand mixer on high speed, scraping down the sides as needed, until the mixture is thickened and pale yellow, about 2 minutes. (Whisking by hand also works. In a stand mixer, the yolks might not have enough volume for the whisk attachment to reach them in the bottom of the bowl.) Gradually stir in the almond flour mixture with a wooden spoon, followed by the shredded carrots and vanilla. The batter will be quite thick at this point; set aside.

Step 4

Using clean beaters, whip the egg whites with the salt in a medium bowl with the hand mixer set on high speed until they form stiff, but not dry, peaks. Using a rubber spatula, stir about 1/4 of the whites into the carrot mixture to lighten it. Fold in the remaining whites. Transfer the batter to the prepared pan and spread into an even layer.

Step 5

Bake until the cake is golden-brown and has shrunk slightly from the sides of the pan, about 1 hour. Cool the cake on a wire rack for 30 minutes. Remove the sides of the pan and let cool completely. If possible, wrap the cake in plastic wrap and let stand for at least 12 hours before serving.

Step 6

Make the mascarpone cream: One hour before serving, stir the mascarpone and powdered sugar together in a small bowl until combined. Let stand at room temperature for about 1 hour to remove its chill.

Step 7

Just before serving, sift powdered sugar over the cake. Slice and serve with a dollop of the mascarpone cream, topped with finely grated orange zest if desired.