Line 18 muffin tins (1 1/2 standard 12-cup trays) with paper liners.
In a large microwave-safe mixing bowl, melt 2 tbsp butter, dark chocolate and cocoa powder. Stir frequently to fully incorporate cocoa and to prevent scorching. Add 2 cups mini marshmallows and microwave for 1-2 minutes, until fluffy and melted. Add in 3 1/4 cups rice krispies and stir to combine, making sure chocolate covers the whole batch. Stir in mini chocolate chips and divide mixture evenly among prepared muffin tins, filling each 1/2 way up.
In a large microwave-safe mixing bowl, melt 2 tbsp butter and mini marshmallows in microwave for 2-3 minutes, until marshmallows are fluffy and butter is completely melted. Add in vanilla and remaining 3 1/4 cups rice krispies and stir to coat every rice krisp (feel free to scrape in a little bit of vanilla bean, if you like).
Divide evenly among chocolate-filling muffin tins, filling each the rest of the way up.
Chill in the refrigerator for 15 minutes or let set at room temperature before serving.
Store in an airtight container at room temperature.
*Note: I also had one all-chocolate one leftover, but I might have simply added a spoonful of extra rice krispies to my mixing bowl by accident. Even so, don’t worry if you want to go into more than 18 muffin cups. Make the treats as big or as small as you like.
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