Grease a 9 by 13 inch baking dish and set it aside. Melt the butter in a large pot over medium heat.

Add the mini marshmallows to the pot and stir until fully melted and smooth. Remove the pot from heat.

Stir the Rice Krispies cereal into the marshmallow mixture until evenly coated. Divide the mixture in half. Leave one half plain and tint the other half with black gel food coloring until it reaches a dark shade.

Press the plain mixture into the prepared dish in an even layer. Press the black mixture on top in a second even layer. Let the slab cool completely.

Cut the cooled slab into 12 rectangles of equal size. These will form the walls and roofs of the houses.

Melt the dark chocolate chips in a microwave-safe bowl in 20-second bursts, stirring between each burst until smooth.

Stack three rectangles per house, alternating plain and black pieces, using a small amount of melted chocolate between each layer to hold them in place. Repeat to make four houses.

Drizzle remaining melted chocolate over the tops and sides of each stack. Add Halloween sprinkles while the chocolate is still soft.