In a stand mixer, beat the softened butter with the dulce de leche until smooth and creamy.
Place one wafer layer on a serving plate and spread with a thin layer of cream. Repeat with the remaining wafers and cream, finishing with a layer of cream on top.
Sprinkle the chocolate over the cake or drizzle with melted chocolate, if using.
Refrigerate for at least 2 hours before serving. For the best texture, chill overnight until the wafers soften and absorb the cream.