Line a large rimmed baking sheet with waxed paper. Melt chocolate (see âÂ€ÂœMelting Chocolate: Be Gentle,âÂ€Â? below). With a heatproof spatula or wooden spoon, stir in peanuts and raisins.
Scrape mixture onto prepared baking sheet and spread to about a 1/2-in. thickness. Chill bark until firm, about 1 1/2 hours. Break or cut into chunks. Store in an airtight container at room temperature for up to 2 days or in the refrigerator for up to 2 weeks.
Melting chocolate: Be gentle. Fill a saucepan with 2 to 3 in. of water. Put finely chopped chocolate in a heatproof bowl that will fit over pan (the bottom of the bowl should not touch the water); set bowl aside. Bring water to a boil, turn off heat, then set bowl over pan. Use a heatproof spatula or wooden spoon to stir the chocolate frequently and encourage even melting. Once the chocolate is melted, stir well and use immediately.