How to Make It
Line a small baking sheet with parchment paper. In a medium saucepan, cook the sugar with the water over moderate heat, stirring just until dissolved. Simmer undisturbed until a light amber caramel forms, about 5 minutes. Stir in the cashews and sesame seeds and cook for 1 minute; immediately pour the caramel onto the lined baking sheet and refrigerate until set, about 15 minutes. Chop the brittle into 1/2-inch pieces.
Pour the tempered chocolate into molds, filling them about halfway. Sprinkle the brittle on top and refrigerate until set, about 15 minutes. Unmold the chocolates and store at room temperature for up to 2 weeks.
EQUIPMENT Plastic chocolate molds are available from Broadway Panhandler, 866-COOKWARE.
ALTERNATIVE If you don't want to use molds, pour the melted chocolate onto a parchment-lined baking sheet and sprinkle with the toppings; let set, then break into pieces.
This recipe will be most delicious if you start with excellent chocolate. Look for chocolate bars from Scharffen Berger or another good chocolate maker with at least 55% cacoa content for a sweeter brittle or as much as 80% if you prefer something more bitter.
How To Temper Chocolate To temper 1 1/2 pounds of bittersweet or milk chocolate, set a large bowl over a pan of simmering water. Add 1 pound of coarsely chopped chocolate to the bowl and stir occasionally until melted and an instant-read thermometer registers between 112° and 118°. Remove the bowl from the pan. Add the remaining 1/2 pound of chocolate and stir until melted and the thermometer registers between 88° and 90°. Use immediately.