In a saucepan, bring the cream and granulated sugar to a boil. Then take off the stove and gently stir in the egg yolks.
Return to low heat, and stir for a few minutes until the mixture gets thick and creamy. Do not return to a boil and take off the stove as soon as the mixture has thickened. Cover with plastic wrap and leave to cool.
Whisk the egg whites until stiff and gently fold in the powdered sugar. Gently stir in the ground almonds and pour the mixture into a 10 inch springform baking tin.
Bake at 150°C/300°F for approximately 25 minutes. Remove from oven and set aside to cool.
Whisk the butter until creamy and add the egg cream a spoonful at a time, until all of it has been incorporated. It takes some time for the cream to become smooth and spreadable, so an electric whisk will be the best choice here.
Spread the cream on top of the cooled base and sprinkle with the almond slices.
Tip: If you like the cream soft, serve right away. If you prefer it hardened, chill in the fridge before serving.