Sesame Seed Toffee

Note: Exercise caution when working with sugar syrups cooked to a high temperature. Don’t leave the stove, keep the dogs and kids out of the kitchen, stay off the phone, and if the doorbell rings, stay put with your pot of sugar and butter!
Lightly butter a 11½- by 7½- by 7/8-inch aluminum baking sheet.
In a bowl, combine the butter, sugars, cream, and corn syrup. Place the mixture in a six- to eight-inch heavy-bottomed saucepan and cook over high heat until the mixture reaches 280°F on a candy thermometer, 15 to 20 minutes. Immediately remove from the heat. Stir in two tablespoons of the sesame seeds. Pour the toffee out into the baking sheet. You now have no longer than four minutes to start cutting the toffee.
Using a buttered chef’s knife, cut the toffee into 1½- by 1½-inch squares. Work quickly!
Once the toffee has been cut, place the pieces on a Silpat or parchment paper-lined baking sheet. Temper the chocolate. (Find instructions at charlestonmag.com/tempering_chococate.) Using a dinner fork, dip the toffee pieces into the tempered chocolate, which should be at 87°F. Return the dipped toffee to the baking sheet. Sprinkle it with the remaining sesame seeds. Leave until the chocolate sets up.
Store the toffee in an airtight container, layering parchment or waxed paper between them. They will keep for two weeks. Do not refrigerate.