Make Chocolate Madeleine Batter - Melt butter in the microwave or small saucepan and set aside to cool.

With a hand-held or stand mixer fitted with the whisk attachment, whisk eggs, sugar and vanilla on high speed for 6 to 8 minutes (set a timer!). The mixture will be thick, pale in color, and form ribbons when you lift the beater(s).

Sift the dry ingredients into the egg/sugar mixture and with a rubber spatula, gently fold just until the ingredients are combined. Do not overmix.

Finally, add your oil and cooled melted butter (should still be in liquid form) into the batter and incorporate just until combined. Remember not to overmix it as you do not want to deflate all the air bubbles. Place a piece of plastic wrap directly onto on the batter to prevent a skin from forming. Chill for at least 2 hour.

When you are ready to bake, melt 1 to 2 tablespoons of butter and generously grease your madeleine pan and then place in the freezer for 10 minutes.

Preheat the oven to 425ºF (218ºC).

Remove pan from the freezer. Scoop a heaping tablespoon of batter and place into the middle of each cavity. Don't worry about spreading it to the corners. The batter will spread and fill out as it bakes in the oven. If you only have leftover batter, place it back into the fridge.

Bake at 425ºF (218ºC) for 3 minutes and then lower the temperature (without opening the oven door) down to 350ºF (176ºF) and bake for an additional 6 to 8 minutes. It's ready when the center of the hump springs back when gently pressed. Keep in the pan for several minutes, then transfer to a cooling rack to cool.

Clean, grease and freeze your pan again. Turn the heat back up to 425ºF and bake off the rest of the batter. 

Make your Chocolate Shell - Chop the chocolate and transfer to a heatproof bowl. Place the bowl over a small pot of simmering water, making sure the bottom of the bowl doesn't touch the water. Once your chocolate is completely melted, carefully transfer the bowl onto the counter.

Make sure your Madeleine pan is clean for this next step. Add about 1 1/2 to 2 teaspoons of melted chocolate into the center of each cavity. Gently press the scalloped side of each madeleine into the chocolate. Freeze for about 30 minutes or until the chocolate is solid.

Release madeleines from the pan. They should release pretty easily once they are fully set. If they do not come out easily, freeze for another 5 minutes and try again. Let the madeleines come back to room temperature before enjoying!