Arguably, this is the best idea for a combination anyone has ever had.
Place chocolate in a bowl set over (not in) a saucepan of simmering water. Stir occasionally, until melted, 3 to 5 minutes. Remove from heat.
Line a baking sheet with waxed paper. One at a time, dip each strawberry in chocolate, twirling to coat; then sprinkle chocolate-covered portion with pistachios, if using, and place on waxed paper.
Chill chocolate-dipped strawberries at least 15 minutes to set chocolate. (Strawberries should not be stored in refrigerator longer than 1 hour as condensation drops may collect on the chocolate.)