Makes 16 two-inch squares
4 tablespoons (½ stick) butter, plus extra for greasing the pan
1 pound semisweet or bittersweet chocolate
1 (14-ounce) can sweetened condensed milk
1/8 teaspoon salt (optional)
½ cup chopped nuts (optional)
1. Butter an 8-inch-square baking pan. Line with parchment or wax paper, letting edges of paper hang over sides of pan.
2. In a microwave on low power, melt the chocolate slowly in multiple bursts. You want it melted, but not hot. (You can also use a double boiler or a metal bowl set over not in simmering water.
3. Add all other ingredients except the nuts. Mix gently until well combined.
4. Mix in nuts, if using.
5. Scrape mixture into prepared pan.
6. Refrigerate until set, about 4 hours or overnight. Lift fudge on paper out of pan and use a large knife to cut into squares.