Chop the chocolate block into small pieces using a serrated knife (I break the chocolate into chunks if I can).
Put ¾ of the chocolate into a microwave-safe bowl, then melt in 20-30 second bursts until the chocolate is almost melted. Using a digital thermometer, make sure the melted chocolate doesn’t go over 120°F (for milk and white chocolate, that limit is 105°F).
Once the chocolate is melted, add the reserved chocolate (1 piece at a time) and stir until the chocolate cools to 91°F. This is the step that takes the most time and is the most aggravating...I’ll check the temperature and react the same (“it’s not cool enough yet?!?”). Have patience…it’ll get there. When (finally) the chocolate reaches the correct temperature. it’s ready for use.
Keeping the chocolate in the correct temperature range (86° to 91°F for dark chocolate; 84° to 86°F for milk and white chocolate) requires a bit of ingenuity. Again, there are numerous ways to go, but I use a neat trick I found on the interweb…place your bowl on a regular heating pad turned to low/medium heat and covered with a dish towel. Check your temperature occasionally to be sure you’re still within range.