In a heavy medium saucepan, melt chocolate and butter over low heat, stirring
often.
Stir in sugar, corn syrup and the 3/4 cup Half-and-Half. Stir over medium-low
heat until mixture comes to a boil. Simmer for 4 minutes without stirring; set aside.
In a small bowl, beat eggs until blended.
Stir in the 1/2 cup hot chocolate mixture.
Cook and stir over medium heat until slightly thickened, about 1 minute.
Cool to lukewarm.
Stir in vanilla extract, the 1 1/2 cups Half-and-Half and whipping cream.
Pour into ice cream canister.
Freeze in ice cream maker according to manufacturer's directions.