Place the coconut oil in a medium microwave-safe bowl. If it's solid, microwave it to melt for 20-30 seconds.
Use a hand whisk or a rubber spatula to mix in the cocoa powder, vanilla, and stevia.
If your nuts are coarsely chopped, place them in a resealable bag and go over them back and forth with a rolling pin to create a finer chop. Use a rubber spatula to mix the chopped nuts into the chocolate mixture.
Using a teaspoon, transfer the mixture to a silicone cordial mold, which you can get on Amazon.
Freeze the chocolate for 20 minutes, then release it from the mold. Store it in the fridge, in an airtight container lined with wax paper, for up to a week.
Enjoy this chocolate straight out of the fridge - it's melty. It sets better the next day, so consider making it a day ahead.
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Notes
This chocolate is melty because of the coconut oil. I don't mind the meltiness, and I love the flavor of virgin coconut oil. But if you suspect this would be an issue for you, use melted food-grade cacao butter instead of coconut oil and omit the vanilla extract (the water it contains can cause the chocolate to seize when cacao butter is used). Alternatively, make it the day before you plan on enjoying it. Its texture greatly improves after a full night in the fridge.
If you like peanuts, you can use them instead of walnuts or pecans. If you like a sweet-salty flavor combination, you might enjoy using salted peanuts.
This recipe makes about 4.5 ounces of chocolate or 10 cordial pieces. I consider one serving as two pieces, which is about 1 ounce.
You can store this chocolate in an airtight container in the fridge for up to a week. Since it's quite melty, it's best to enjoy it straight out of the fridge. I don't recommend freezing this chocolate.