In medium-size saucepan, heat oil over medium-high heat. Add celery, carrot, red pepper and scallions and cook, stirring, 5 minutes. Add potato, salt, pepper, Old Bay seasoning and thyme. Cook an additional 2 minutes.
Stir in 2 cups of the milk and 1/2 cup water. Cover and bring to a simmer. Reduce heat to medium low and simmer for 12 to 14 minutes or until vegetables are tender.
Once vegetables are softened, stir in corn and crabmeat. In a small dish, stir the remaining tablespoon milk into the cornstarch. Add to pot, stirring; cook 3 minutes, or until thickened. Cool slightly, then serve. Makes 2 servings.