Simmer to reduce liquid
Whisk in a cornstarch slurry
Whisk in a flour slurry
Make a roux
Add beurre manié
Stir in arrowroot
Stir in tapioca starch
Use potato starch
Add mashed vegetables
Add tomato paste
Add cream or cheese
Blend in nuts or seeds
Puree part of the sauce
Add egg yolk carefully
Use xanthan gum
Add gelatin
Stir in breadcrumbs
Add instant potato flakes
Let the sauce cool slightly to thicken