Butter the bottom of an 8-inch to 9-inch square baking pan.

Line the pan with a square of parchment or wax paper.

Place all ingredients (chocolate, butter, cinnamon, cayenne, nutmeg, salt, sweetened condensed milk) into a metal bowl.

Set the bowl over a pan of gently simmering water.

Stir the mixture occasionally to melt.

Spread the thick mixture evenly into the prepared pan.

Chill the fudge until firm, ideally overnight.

Run a warm knife around the edges of the pan to loosen the fudge block.

Flip the fudge block over onto a cutting board.

Remove the parchment or wax paper.

Cut the fudge into 1-inch squares.