Place the semi-sweet chocolate chips in a large mixing bowl or glass measuring cup, then place a fine-mesh strainer over the bowl. Set to the side.
In a medium saucepan, whisk together the cocoa powder, cornstarch, sugar, and salt until well combined. Slowly whisk in ½ cup milk to combine. Once combined, slowly drizzle in the remaining milk and the heavy whipping cream, whisking to combine.
Place the saucepan over medium heat and bring to a gentle boil, whisking constantly. Reduce heat to low and simmer until slightly thickened (the mixture should coat the back of a spoon) and the sugar is fully dissolved, whisking constantly. ~1-2 minutes.
Remove the chocolate milk mixture from the heat and pour it through the strainer over the chocolate chips. Add the vanilla extract and stir until the chocolate chips have melted.
Let the mixture cool for 5-10 minutes and then transfer to popsicle molds.
Freeze until solid, about 6 hours.
To remove a fudgesicle from the mold, place the mold under running hot water for a few seconds.
Notes
Dairy-Free Fudgesicles: Replace the whole milk and heavy cream with a 15-ounce can of full-fat coconut milk and use your favorite dairy-free chocolate chips. Heavy Cream: You can replace the heavy cream with additional whole milk, but heavy cream makes these treats taste incredibly rich and fudgy.Corn-Free Fudgesicles: Replace the cornstarch with arrowroot powder or tapioca starch.Storage: These can be stored in the freezer for up to 3 months. That said, I find they are best enjoyed within 30 days of preparation. Nutrition has been calculated using heavy cream, Guittard chocolate, and whole milk.