Pour the sweetened condensed milk in a large microwave-safe bowl. Roughly chop the almond bark and place it in the bowl. Microwave in 1 minute increments, stirring in between, until the mixture is totally smooth.
Meanwhile line an 8x8-inch baking dish with foil. Once the fudge mixture is smooth, stir in the pistachio extract and chopped pistachios. Add green food coloring if desired.
Pour the fudge into the prepared pan and place in the refrigerator for at least one hour. Then flip the hardened fudge out onto a cutting board and peel off the foil. Trim the edges and cut into 49 squares. Keep in an airtight container at room temperature, or in the freezer!
Almond extract has a similar flavor and can be substituted, but the pistachio extract is wonderful!