Cook butter (1 tablespoon), cream, chocolate, sugar, vanilla, cinnamon, cayenne, and a pinch of salt in a 1- to 1 1/2-quart heavy saucepan over low heat, stirring constantly, until chocolate is melted and mixture is smooth, 1 to 2 minutes. Remove from heat and whisk in egg until combined. Fold in bread cubes and let stand 5 minutes.