In a large pot, heat oil and melt butter. Add the onion and sauté until soft, not brown.
Add flour and stir for 1-2 minutes until smooth.
Add the stock gradually, being sure to stir constantly to incorporate the flour.
Add the potatoes and corn. Bring to a boil, reduce heat and simmer for 30 minutes. Remove from heat.
Transfer half of the soup to a separate bowl. Ladle this soup, a little at a time, into a blender. Puree until creamy smooth.
You can return the soup puree from the blender back into the pot as you go.
When done, add milk, salt, pepper and Tabasco to taste.
Adjust the spiciness of the soup with the Tabasco. Return to heat, bring to a desired temperature and serve. Garnish with chives.