I recommend using a double boiler on the stove. Simply fill a saucepan with a few inches of water and bring to a simmer on the stove over low heat. Place the chopped chocolate or chocolate chunks in a heatproof glass bowl that fits snugly over the saucepan. The bowl should be at least 3 inches above the boiling water. Stir the chocolate regularly for even melting, and once melted, remove from the heat. If that sounds like too much work for you (I get it), you can safely melt the chocolate in the microwave, but be sure to do it in short intervals. I usually heat the chocolate chunks for 25-30 seconds, give it a stir with a rubber spatula, and repeat two more times until the chocolate is almost fully melted, then give it a final stir to melt the remaining chocolate.