1. Preheat the oven to 325°F (160°C). Butter an 8in (20cm) round cake pan and line the bottom with a round of parchment paper.

2. Cook the carrots in a little water about 15 minutes, or until very tender. Drain and purèe with the orange juice; you should have ½ cup of purèe.

3. Beat the egg yolks, vanilla, and orange zest in a large bowl with an electric mixer on high speed. Gradually add the sugar, mixing until it becomes very thick. Stir in the carrot purèe and almond flour.

4. In a clean, dry bowl, with clean beaters, beat the egg whites until stiff, then fold into the batter. Spread in the pan. Bake for 30 minutes or until a toothpick inserted into the center comes out clean.

5. Transfer to a wire rack and cool for 10 minutes. Invert onto the rack, peel off the paper, and cool completely. Sift confectioner's sugar over the top before serving, if desired.