1 tablespoon cornstarch dissolved in 1 1/2 tablespoons water
In a medium saucepan, combine the orange juice with the honey. Scrape the seeds from the vanilla bean into the saucepan and add the bean. Bring to a boil over moderate heat, stirring to dissolve the honey, about 2 minutes. Add the blueberries and blackberries and cook just until softened, about 2 minutes. Gently fold in the raspberries. Stir the cornstarch slurry and add it to the saucepan. Simmer the compote until thickened and glossy, about 2 minutes. Discard the vanilla bean. Serve warm.
The compote can be refrigerated overnight. Reheat gently before serving.