Sift the cocoa powder into a small bowl. This helps to prevent lumps.
Place a pot filled a third of the way with water on a burner and set the heat to medium-high. Place a large pyrex or metal bowl on top. Make sure the water isn't touching the bottom of the bowl.
Add the cocoa butter or coconut oil to the bowl and stir occasionally until all melted.
Turn the heat down to medium-low. Then stir in the cocoa powder. Then add in the milk powder and stir until completely incorporated. Follow that up with the powdered sugar which is added a third of it at a time until all incorporated. If you want it less sweet don't add in as much, or if you want it completely sugar-free, leave it out altogether.
Once all the ingredients are combined turn the heat completely off. Keep stirring for about 5 minutes.
After the 5 minutes are up, take the bowl off the pot of hot water and set it somewhere like a counter or table with a hot pad. Keep stirring for another 5 minutes.
Once done, pour the chocolate into your chosen mold, or even ice cube trays. Allow it to sit at room temperature for about 30 minutes. Then it can go in the fridge for about 30 minutes.
Once the chocolate sets, you can eat it. Remove it from the mold and give it a taste. It will probably taste a little grainy or gritty. I don't really mind the little bit of "gritty" taste. If you are expecting this to taste exactly like store-bought chocolate, you will be disappointed.And there you go, fun homemade chocolate that only requires 4 ingredients. Enjoy!