Simmer uncovered to reduce excess liquid
Whisk in a cornstarch slurry
Whisk in a flour slurry
Add a beurre manié
Stir in tomato paste
Add mashed vegetables
Blend in cooked beans or lentils
Add cream, yogurt, or sour cream
Add grated cheese
Use arrowroot or tapioca starch
Add a roux
Puree part of the sauce
Add a small amount of xanthan gum
Let the sauce cool slightly to thicken
Add ground nuts or nut butter