In a medium saucepan, heat the olive oil over medium-high heat. Add the garlic and brown slightly, approximately 1 minute. Add in the cornstarch and stir until the garlic is coated. Pour in the wine and beef stock.

Allow the mixture to reduce by half, approximately 5-7 minutes. Stir in the butter and rosemary and season with salt and pepper to taste.

Keep warm over low heat until ready to serve.