Now, the cake batter. Combine the yolks, vanilla and about 1/4 of the sour cream lightly.
Bake for 40-50 minutes or until a skewer inserted in the middle comes out clean or until golden brown. When you press the cake down slightly in the middle, it must spring back.
Since one can directly heat the butter and sugar on the cast iron skillet on the stove and it helps caramelize the sugar while baking, a cast iron skillet is preferred. If you are using a springfoam pan, then wrap the side with aluminium foil to prevent leakage. When you start heating the oven, place an aluminium sheet in the oven. Place the springfoam pan on the aluminium sheet when ready. I had a smaller skillet and therefore used a cake pan. The cake will last for 3 days in the fridge and 1 day at room temperature.