For the cream; Place butter, dulce de leche and nutella together and whisk until everything is well combined.
Combine whipping cream together with condensed milk. Unroll the cake and spread the cream mixture over the cake. Let the mixture soak for a few minutes while you work on the cream.
Spread 3/4 of the cream on to the inside of the roll. At one of the edges places Ferrero chocolates side by side.
Spread 3/4 of a cup of crushed hazelnuts over the cream. Roll the cake tightly together. Spread the remaining cream and hazelnuts over the top of the cake.
Melt chocolate in a microwave, be sure to stir it every 10 seconds. Place it in a ziplock bag, cutting an edge of the corner, drizzle the roll with the chocolate. While the Ferrero candies are still wrapped, cut them in halves and decorate the top.
Let the cake be refrigerated overnight. Depending on your preference, you can serve it while it is very cold or after letting it sit in a room temperature for 10-15 minutes.