Grease a loaf pan and a deep 3-quart microwave-safe casserole dish with the 2 tablespoons butter.

Combine sugar, milk, chocolate, syrup and salt in the casserole dish. Cover dish with plastic wrap.

Heat sugar mixture in the microwave oven on High for 5 minutes; stir well. Remove plastic and continue to cook in the microwave until the chocolate mixture reaches soft-ball stage, about 235 degrees (113 degrees F), 4 to 7 minutes. Stir again thoroughly and continue cooking on High for 6 to 7 minutes. Lie butter atop the chocolate mixture and set aside to let it melt as the chocolate mixture cools.

Stir vanilla into the cooled chocolate mixture; beat continuously with a wooden spoon until the fudge is thick and starts to lose its shine. Fold nuts through the fudge; spread quickly into the prepared loaf pan.

Let fudge sit until set, 30 to 40 minutes. Cut while still slightly warm.