Heat 1 teaspoon oil in a large nonstick skillet over medium heat. Add shallots; cook 5 minutes or until golden brown. Stir in juice. Bring to a boil over medium-high heat, and cook until reduced to 1 cup (about 6 minutes). Remove from heat; cool.
Place the grapefruit juice mixture, cilantro, sugar, and pepper in a blender; process until smooth. With blender on, slowly add 2 tablespoons oil; process until smooth.