Simmer the stock uncovered to reduce and concentrate it
Add a cornstarch slurry and cook until thickened
Add a flour slurry and cook until smooth and thick
Whisk in a beurre manié
Stir in a roux made separately
Add gelatin-rich ingredients like chicken feet, wings, or skin and simmer longer
Blend in pureed vegetables such as potatoes, carrots, or onions
Add instant potato flakes in small amounts
Use xanthan gum in very small amounts
Strain, chill, and remove excess fat before thickening
Reduce the stock before adding salt or seasonings