In the same large pot or Dutch Oven you cooked the vegetables, melt the remaining butter over medium low heat. Add flour to the melted butter and whisk constantly until flour is cooked through, about 1-2 minutes, and begins to resemble a thick paste. Do not leave unattended and do not allow the roux to burn .Add milk slowly, whisking constantly until smooth. Pour in the chicken broth and continuing whisking to incorporate all the ingredients well.
Add the softened cream cheese in pieces to the roux. Stir cream cheese until it has dissolved and thickened into the sauce. About 1 minute.
Add turmeric, dry mustard, paprika and garlic salt. Whisk until well blended.
Once sauce is thick, on very low heat, add cheddar and parmesan and whisk in until melted.
Finally, if needed, add salt and pepper to taste and water or chicken broth if sauce is too thick to pour. Cover pot, remove from heat, but keep warm.