adapted from Dorie Greenspan featured in Bon Appetit June 2006
1/2 cup sugar
2 tablespoons cornstarch
1 1/4 teaspoons cinnamon
2 cups whole milk, divided into 1/4 and 1 3/4 cups
5 ounces bittersweet chocolate, finely chopped
1/2 cup heavy cream (I used whole milk)
1/3 cup coarsely chopped toffee bits/candy bar pieces (I left these out)
Whisk sugar, cornstarch, cinnamon, and salt in heavy medium saucepan until blended. Gradually add 1/4 cup milk, whisking until cornstarch is dissolved. Whisk in remaining 1 3/4 cups milk. Whisk over medium-high heat until mixture thickens and comes to boil, about 6 minutes. Reduce heat to medium and cook 1 minute longer, whisking occasionally. Remove from heat; add chocolate. Let stand 1 minute, then whisk until melted and smooth.
Transfer gelato base to medium bowl. Mix in cream. Place bowl over large bowl filled with ice and water and cool, stirring often, about 30 minutes.
Process gelato base in ice cream maker according to manufacturer's instructions, adding toffee during last minute of churning. Transfer to container; cover. Freeze at least 3 hours and up to 2 days.