Cake: (based loosely on Foolproof Sponge Cake in The New Best Recipe)
1 teasp baking powder
1/4 teasp salt
3 tblsp butter
1/2 cup sugar
1/2 cup almond meal or almond flour
grated peel of one lemon
Preheat oven to 350 and thoroughly butter or spray a bundt pan. Sift together flour, wheat gluten, baking powder and salt. Melt the butter and set aside to cool. Separate 3 eggs. Beat the 3 egg whites, adding 1/4 cup sugar when they are frothy, until they form soft peaks. Beat the egg yolks and remaining eggs in a separate bowl until light-colored and thick. Beat in the almond meal and grated lemon peel. Fold in the beaten egg whites. Sift the dry ingredients over the egg mixture and fold in gently. Pour the melted butter along the side of the bowl and fold in gently. Immediately pour the batter into the prepared bundt pan. Cook for 45 minutes or until the top springs back when touched. Cooking time would be more like 25 minutes if you bake it in two layer pans. Cool in the pan at least 10 minutes, then invert onto a rack and cool completely.
Lemon curd: from The New Best Recipe
2 eggs and 1 egg yolk
1/4 cup sugar
1/3 cup lemon juice
2 tblsp butter, cold or room temperature
2 tblsp heavy cream
a pinch of salt
Whisk the eggs until uniform in a non-reactive pan, then whisk in the sugar. Heat the lemon juice until hot but not boiling (I do this in the microwave in the glass measuring cup) and pour slowly into the eggs, whisking all the time. Put the pan on medium low heat and cook, stirring constantly with a wooden spoon, until it thickens. Stir in the butter quickly to stop the cooking, then stir in the cream and salt. Cool to room temperature.
1/2 teasp unflavored gelatin
1 recipe (above) of lemon curd
1 cup heavy cream, cold
Put the gelatin in a small bowl with 1 tblsp cold water. Wait a few minutes until it no longer looks white. Put the bowl into a pan of hot water and warm until the gelatin dissolves completely. Set aside to cool. Whip the cream. Stir the gelatin into the room temperature lemon curd. Fold the lemon curd into the whipped cream. Chill for at least a couple of hours before assembling the cake, overnight would probably be better.
If you made the cake in a bundt pan, slice the cake horizontally into the number of layers you want. If you want a surprise filling, cut it into two layers and partially hollow out the cut sides of the two layers with a grapefruit knife to make a channel for the filling. Fill with the lemon mousse. I use a bundt pan because I think it is attractive enough with no icing, but you could dust the finished cake with powdered sugar or add a lemon glaze. I spread filling over the top because I had so much left over. If you make the cake in layer pans, you can slice each layer in half horizontally, spread lemon curd between each layer to make a four layer cake, and then frost with the frosting of your choice.
If you aren't interested in reducing carbohydrates you can double the amounts of sugar, leave out the almond meal, and use 1 1/4 cups of white flour instead of the whole wheat flour, wheat gluten, and almond meal.