For the egg liqueur tart, beat egg whites until stiff peaks form. Beat yolks, oil, water, sugar and hazelnuts in a mixing bowl until foamy. Stir in the flour mixed with baking powder and fold in the beaten egg whites.
Pour the batter into a floured and buttered cake tin (26 cm) and bake at 180°C for about 45 minutes.
Cut the cooled cake in half and fill with the jam.
Whip the cream with the cream stiffener until stiff, fill 1/3 into a piping bag, spread the remaining whipped cream on the edge and on the surface of the cake.
Use the remaining mixture in the piping bag to pipe a border with rosettes.
Soak the gelatin in cold water, then dissolve in a little eggnog and mix with the remaining eggnog and spread on the cake.
Refrigerate the eggnog cake until the eggnog has set.