Start by combining your base ingredients in the crockpot. Add the all-purpose flour, 1½ cups of the white granulated sugar, 1 cup of whole milk, melted salted butter, 6 tablespoons of cocoa powder, and vanilla extract directly into your 6-quart or larger slow cooker. Use a whisk or wooden spoon to mix these ingredients thoroughly until you have a smooth, lump-free batter.

Next, prepare the topping mixture that creates the magic. In a separate mixing bowl, combine the remaining 2 cups of white granulated sugar with ½ cup of cocoa powder. Whisk these dry ingredients together until they're well blended and there are no lumps of cocoa powder.

Take this dry sugar and cocoa mixture and evenly sprinkle it over the top of the batter in the crockpot. Don't stir it in – this layer will help create the separation between the cake top and the gooey bottom as it cooks. Make sure you distribute it as evenly as possible across the entire surface.

Cover your crockpot with the lid and cook on high for 3-4 hours. You'll know it's done when the top has set up and looks cake-like, though it will still have a slightly wet appearance. The edges might look darker, almost burnt, but that's normal – it's just the rich chocolate color, not actual burning.

Let the crockpot chocolate cake cool for about 5-10 minutes before serving. Scoop generous portions into bowls and top with a scoop of vanilla ice cream. The ice cream will start to melt into the warm chocolate, creating an incredible sauce.