Combine ham and chicken bases in a saucepan and whisk until no lumps appear.
Melt 3 tablespoons margarine in a stockpot and saute onions until transparent. Add potato and pepper and stir until completely mixed. Add chicken and ham stock and stir until mixture begins to boil.
While mixture is boiling, microwave the remaining 3 tablespoons margarine 20 seconds or until melted. Whisk flour into melted margarine and stir until it forms a roux into the stock. The soup will start to thicken. Bring soup back to a boil, then slowly add the milk, whisking constantly.
When milk is incorporated remove from heat. Garnish with chopped parsley and serve. You can also add bacon bits, shredded cheese, and sliced scallions on the soup.
. The Houston Chronicle suggests that the bases may not be available in supermarkets; they suggest that you use chicken broth and a piece of ham.