You sure can! Using a double boiler to make fudge and candy is an excellent idea as it stops the ingredients from getting too hot and cooking too quickly, while also ensuring that no steam or other things that might ruin your mixture are able to penetrate. There are loads of recipes online for how to make fudge or candy using double boilers. And even when the recipe doesn't specifically call for it, we found that every time we used a double boiler in our candy-making, the results were far better than they were before we invested!\r