1. In a large saucepan, bring 1/2 inch of water to a boil over high heat.
2. Add the squash and onion.
3. Lower the heat and simmer, covered, for 3 to 5 minutes or until squash is crisp-tender. Drain.
4. Meanwhile, in a small saucepan, stir together the sour cream and flour. Stir in the milk, dill, salt, and red pepper.
5. Cook and stir over low heat until heated through (do not boil).
6. Pour over the vegetables; stir until mixed.