Add the dark chocolate broken into roughly 1 cm pieces and the cut butter into a heat resistant container and microwave at 600 W for 1 minute.
This is how the mixture should look when taken out of the microwave.
Mix the chocolate and butter with a whisk, add the sugar, pancake mix, cocoa powder and egg, and mix again.
Lightly grease a gratin dish with butter (not listed) and pour in the mixture from Step 3. You could also use ramekins.
Add 200 ml water to the frying pan and bring to a boil. Stop the heat and put the gratin dish into the pan.
Put the pan on a medium heat, boil the water and cover with a lid. Turn down the heat (but still high enough to keep the water simmering) and steam the mixture for about 10 minutes whilst keeping an eye on it.
The heat will vary depending on the thickness of your frying pan and the type of stove you're using (gas, electric, etc). Steaming time may also vary so adjust as necessary.
Make sure that water doesn't get into the cake while cooking, and also watch that the water level doesn't drop.
Remove the lid and check to see if the gateau au chocolat is done by inserting a toothpick into the center. If it comes out clean, cover with a lid and remove from heat.
Steam for a further 5 minutes with the lid.
Take off the lid and leave the gateau au chocolat to cool in the dish. Once the dish is cool enough to touch, remove.
Once the gateau has cooled, use a tea strainer to sprinkle powdered sugar or cocoa powder.
If you sprinkle powdered sugar, it may melt into the cake and turn transparent.
The taste and texture of the cake will differ depending on whether it is cooled at room temperature or in the refrigerator. Feel free to try both results!
If you reduce the steaming time you can make a molten chocolate cake. Refer to "Steamed Molten Chocolate Cake" (Recipe ID: 2483514).
This recipe uses 1 bar of milk chocolate "For Valentine's ♥ Gateau au Chocolat in a Frying Pan" Recipe ID: 2467422
This recipe uses dark chocolate "Gateau au Chocolat in a Silicone Steamer" Recipe ID: 1251677
"Gateau au Chocolat in the Frying Pan" (Recipe ID: 2043406) is made by lining a frying pan with parchment paper and baking the batter inside.
Story Behind this Recipe
I often made gateau au chocolat in a silicon steamer in the microwave and wondered if there was another way. I tried a few methods and came up with this. I always used 40 g of dark chocolate until now, but made a recipe that uses 55 g so that I can use the entire bar.
Choose a frying pan that's large enough to fit the gratin dish. (I used a gratin dish that was 13 cm diameter x 4 cm deep and a frying pan that was 20 cm diameter.) Keep an eye on the gateau and adjust the cooking time accordingly.