Lightly butter a 8x8 inch baking pan.

In a large saucepan over medium-high heat, combine sugar, corn syrup, butter, milk, and chocolate. Bring to a boil and stir to dissolve sugar. Place a candy thermometer into the mixture.

Reduce heat and cook, stirring, until temperature reaches 244°F.

Remove from heat and stir in vanilla.

Pour into buttered pan and let cool completely, about 3 hours.

Turn pan upside down to release caramel, cut into squares, and wrap in pieces of waxed paper.