Process 1/2 cup of the Mulberries in a food processer or blender until pureed. Combine the cornstarch and sugar replacement in a heavy or nonstick saucepan; then gradually add the milk, pureed Mulberries, and lemon juice.
Cook and stir over medium heat until clear and thickened. Remove from heat and stir in remaining Mulberries. Cover and cool to room temperature before using.