Beat yolks and egg at high speed for 20 minutes until very thick and mixture drops from beaters in a thick, smooth stream.
Line 4 cake pans (9 inches - 23 cm) on the bottom, with greased and floured paper.
Divide the mixture in 4. Spoon each portion in a pan.
Preheat oven at 350° F - 180° C. Place pans in oven and bake for 10 to 15 minutes (if 4 can not be baked at the same time, bake 2 first).
Remove from oven. Unmold warm and remove paper.
Use half of butterscotch for layers. Top bottom layer with whipped cream and pour some butterscotch. Repeat with other layers. Finish by covering with whipped cream. Pour butterscoth on top making designs.
Whip cream. Gradually add sugar and continue beating until thick and soft peaks form.
Place sugar in a medium saucepan over low heat stirring with a metal spoon until sugar is dissolved and reaches a caramel color.
Pour immediately the condensed milk and stir until caramel dissolves and thickens to a sauce consistency.
If sauce gets too thick soften with milk or water.
Cool. Use half of the butterscotch for the layers. Pour rest on a sauceboat.