2 pounds bittersweet or semisweet chocolate, finely chopped
4 tablespoons (1/2 stick) unsalted butter, cut into pieces
2, 14-ounce cans sweetened condensed milk
1 teaspoon vanilla extract
Thoroughly coat all inside surfaces of a 9 x13-inch pan with nonstick spray; set aside.
Melt chocolate and butter in double boiler or microwave, stirring until smooth. Remove from heat and stir in condensed milk and vanilla extract. The mixture should be completely smooth.
Scrape fudge into prepared pan. Use rubber spatula or your fingers to coax fudge into corners and into an even layer.
Refrigerate 2 hours or until firm enough to cut. Cut into and 8 x 5 grid to make 40 squares. You can really cut this into any size square you like, or even cut out fancy shapes with cookie cutters.
Refrigerate in an airtight container in single layers separated by waxed or parchment paper for up to 2 weeks.