Preheat oven to 425 degrees and move rack to center position. Prepare foil pans by coating the sides and bottom with 1 tsp. butter in each pan; use your fingers to rub the butter all around. Add 1/2 tsp. flour to each cup and tap to coat the butter with the flour. Get rid of excess by tapping the bottom: only a small amount of flour should be left coating foil pan. Using a double boiler, melt chocolate and remaining butter in a medium bowl. Stir until fully melted. Remove bowl from heat. (How to make a double boiler: In a small pot, add about 2 inches of water and bring to a simmer, place a heat safe bowl on top of the pot. Make sure not to let any water get into the bowl, it will ruin the chocolate. Also, be careful removing the bowl from the pot, the steam from the pot water will be very hot!)

Using a whisk, mix powdered sugar (reserving 2 tsp. for a later step) into chocolate mixture until combined. Next, add liquid eggs, yolks, and vanilla extract and whisk until combined.

Gently stir remaining flour into mixture until just combined. Do not over-mix this: it will cause your cakes to be dense. Portion into foil cups, filling them 3/4 of the way full.

Put on center rack of oven and bake 12-13 minutes. While cakes are baking, add reserved 2 tsp. of powdered sugar to heavy cream jar, affix the lid securely, and shake for 45 seconds. If it is still slightly loose, shake for another 15-20 seconds.

Once the cakes are removed from the oven, let them rest for 2 minutes before unmolding.The outside edges should be set and slightly higher than the middle of the cake. The middle will have a small 'dimple' in it that will look slightly less cooked that the edges. When ready, turn cakes onto plate for serving and top with a heaping spoonful of whipped cream. Serve immediately!