Set oven temperature to 325°F, or 163°C. Take a ramekin. Apply nonstick cooking spray to the ramekin's interior and bottom. Trim the parchment paper so that it fits into the ramekin's bottom. This will facilitate the cake's release and prevent it from clinging to the bottom. Put it aside.
Take a medium sized bowl. In that bowl, mix together the unsalted butter, cream cheese, and granulated sugar using a stand mixer or handheld mixer.
Add eggs in that mixture and incorporate thoroughly.
Add half of the flour and a pinch of salt to the wet mixture. Mix in the dry ingredients with a spatula or you may use a mixer.
Don't overmix when adding the second half of the all-purpose flour; just stir until it's blended.
After that, stir in the vanilla and put the cake batter aside.
Take another medium sized bowl. Blend together cream cheese and granulated sugar in it.
Add one-half of an egg in that mixture. You can do this by whisking the egg into a separate bowl. By weighing each egg, divide it in half using a kitchen scale. You can merely double the ingredients for the top layer and use only half of them for the cakes if you don't have a kitchen scale.
Now add vanilla extract. Mix it thoroughly and set aside the bowl.
Next step is to assemble the cake. For this, take out the cake batter from the pot and divide it evenly among the four ramekins, filling each one approximately halfway. The cake does rise a little, so don't fill it too high. Even out the cake batter on top.
After that, remove the top layer batter and divide it among the four ramekins. Spread the mixture evenly across the top using a spoon. It came out to be two to three tablespoons each of ramekin.
Set the ramekins on a cookie pan and put them on the central rack of the oven.
Bake the California Pizza Kitchen Butter Cakes for 55 to 65 minutes. To test if a cake is done, insert a toothpick into the center of one of them. It's ready if a toothpick inserted into it comes out clean. Increase the baking time if there are clumps and continue until the toothpick comes out clean.
You can let your cakes cool on a baking rack after you take them out of the oven. The cake can be released from the ramekin or pan by running a knife around its edges while it's still warm.
You can remove the warm butter cakes once they have cooled. Delicious Butter cakes are ready. Bon Appetit!