Combine the butter and chocolate chips until melted, either in a double boiler or in the microwave. Mix well, then fold in the eggs, colorful marshmallows, and pecans.
Transfer the mixture into a foil-lined 9x5 inch loaf pan. Sprinkle with powdered sugar and chill until set.
Take the chilled dough out of the loaf pan, discard the foil, and cut into 1/4 inch slices.