Russian Imperial butter cream

This cream can be used for the Russian Imperial dessert or as a filling for other cakes and desserts.

6 egg yolks
3/4 cup (150g) sugar
300g butter, at room temperature
1/4 cup (35g) caster sugar
1 teaspoon vanilla essence
1 small glass cognac (French brandy)

Place egg yolks and sugar in a double boiler over a medium heat and beat until thick. Remove from heat and keep beating until cool.

In another bowl, beat butter and caster sugar with electric mixer until creamy.
Fold in egg mixture and stir in vanilla essence and cognac.