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1
Set the oven at 350F (180C).
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2
Lightly butter two 9-inch (22cm) cake pans, then line each with a round of parchment paper.
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3
Separate the eggs.
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4
Sift together the flour, baking soda, baking powder, cinnamon, and salt.
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5
Beat the oil and sugar in a stand mixer until well beaten, then add the egg yolks one by one.
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6
Grate the carrots into the mixture, then add the lemon juice.
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7
Coarsely chop the walnuts and add them too.
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8
Fold the flour into the mixture with the mixer on low speed.
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9
Beat the egg whites until light and stiff, then fold gently into the mixture using a large metal spoon (a wooden one will knock the air out).
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10
Divide the mixture between the two prepared cake pans, smooth the top gently, and bake for forty to forty-five minutes.
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11
Test with a skewer for doneness.
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12
The cakes should be moist but not sticky.
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13
Remove from the oven and let rest for a good ten minutes before turning the cakes out of their pans onto a wire cooling rack.
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14
To make the frosting, put the mascarpone, cream cheese, and confectioners sugar into an electric mixer and beat until smooth and creamy.
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15
It should have no lumps.
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16
Mix in the orange zest.
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17
When the cake is cool, sandwich the halves together with about a third of the frosting.
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18
Use the rest to cover the top and sides of the cake.
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19
I dont think you need be too painstaking; a rough finish will look more appropriate here.
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20
Cover the top with walnut halves.
