1. Whip eggs plus yolk with sugar until thick and light yellow. Prepare a double boiler with 1-2 inches boiling water in base, and let simmer. Heat the egg-sugar blend over low simmer, and whisk in the lambic. Cook until slightly thickened.
2. Stir in butter and cook, whisking constantly, until mixture is thick, about 8-10 minutes. Remove from heat and let cool. When just warm, whisk in the sour half-and-half. Place in a container with a tight-fitting lid, seal and chill. You may prepare the sabayon a day or two ahead of serving.Adapted from the Fruit Book, Workman Publishing