If you don't have 100% cocoa powder then use milk chocolate drink powder...
Milk chocolate drink (cocoa) powder
3 & 1/2 tablespoons
Butter (or margarine)
Here is a version that swaps the pancake mix for cake flour and baking powder to make the doughnuts. It's recipe ID:2055716.
In a heat resistant bowl, add the butter and heat in a microwave at 600w for 30 seconds till it melts. Preheat your oven to 335°F (170°C).
In a bowl, add the pancake mix, egg, powdered cocoa, sugar, and milk and mix it with a whisk. Also add in the melted butter and mix again one more time.
Take a doughnut mold and lightly coat the insides with vegetable oil. Add in half of the chopped chocolate. Then take the other half and add it to the mixture from Step 2.
Take the mold and spray the inside with spray oil. Holding the mold with both hands, gently tap it a few times to make the surfaces even.
Once your oven has finished preheating, take the tray and put it in. Bake it for about 15 minutes.
On the left is the powdered cocoa version. On the right is the milk chocolate version. They taste very similar to each other.
With the same amount of batter, you can make 12, 5cm diameter doughnuts and 2 cupcakes.
Cleanly removing the doughnuts from the mold (If you are using a silicone tray) Make sure you let them cool before you remove them.
Push up on the bottom of the tray with your fingers. Slowly separate the doughnut from the tray and have them (when done) fall into your hand. Rotate the tray while removing them.
Recipe ID: 1424096 I cut the amount of egg in half and made a fluffy version of these doughnuts.
Recipe ID: 1796892 is a brownie version with walnuts in them.
Story Behind this Recipe
I took the ingredients from a previously submitted recipe ID:1233565 "Steamed Dark Chocolate Cake Made in a Silicone Tray" and I tried transforming it into a baked chocolate doughnut recipe.
You can add the whole bar of chocolate if you want to. The sweetness and richness of milk chocolate varies, so adjust the amount of chocolate you use until it's the flavor you want. (This time I used bittersweet chocolate.)