Place the semi-sweet chocolate chips in a microwave and cook on HIGH for 20-30 seconds at a time, stirring after each. Once the chocolate is mostly melted, add the milk in as well for the final spin in the microwave. (It's also possible to melt these together on the stove over low heat, but that takes longer.)
Stir in the nuts, vanilla, and salt.
Line an 8" square baking pan with wax paper.
Spread the mixture into the pan evenly and chill in the refrigerator for at least 2 hours.
Turn out onto a cutting board and cut into squares.