Bake muffins for 15 minutes. Turn the oven down to 325°F and bake for 3 more minutes. Test muffin with a toothpick to determine if they're cooked (remember the center will be molten). Remove from oven.
Optional: In the microwave, melt the remaining 1/4 cup of ganache by heating for 20 second intervals. Stir between intervals and remove from microwave when it is melted. Use a spoon to drizzle ganache over cooked muffins.