Line baking sheet with parchment paper. In a microwave bowl, melt semi-sweet chocolate and pour onto parchment paper. Freeze for 10 minutes. A few minutes before you are about to remove baking sheet, melt white chocolate in a microwave bowl. Pour white chocolate on top of the semi-sweet chocolate layer. Spread top layer into the bottom layer. While chocolate is still hot, sprinkle pretzel pieces, toffee bits, and salt evenly over white chocolate layer. Freeze for 20 minutes. Break into pieces and keep refrigerated.