For the double boiler, you can easily fake one at home: take a small pot and add a few inches of water. Bring the water to a simmer/boil and add a glass bowl (stainless steel apparently also works, but I’ve never tried) on top of your pot. Make sure the water in the pot is low enough that it doesn’t touch the bottom of your glass bowl. The bowl will get hot, so make sure to use a potholder!
Find it online: https://www.thegarlicdiaries.com/15-minute-peppermint-bark/