STEP 1:
For the custard, whisk butter, sugar & egg yolks over low heat until it thickens. Remove, cover with a lid, & set aside to cool completely to room temperature.
STEP 8:
Frost 1st layer of cake with 1/3 of frosting. Repeat with 2nd & 3rd layer & place 4th layer on top. Frost with reserved whipped cream & top with chocolate shavings.