You can remedy the problem of a thin sauce in a slow cooker by thickening it with cornstarch. High heat usually drives off excess moisture through steam from a sauce, thickening it, but the low heat of a slow cooker coupled with the lid holding steam in the pot prevents the sauce from thickening during the general cooking time. Cornstarch added to the slow cooker binds the excess liquid in the pot to create a thickened sauce. The best time to thicken your sauce is just before you serve the dish.
Remove the lid from the slow cooker and turn the heat to high.
Pull out and set aside large pieces of meat once they have fully cooked.
Strain the liquids from the slow cooker into a measuring cup to help determine the amount of cornstarch to use. Pour the liquid back into the slow cooker and estimate 2 tbsp of cornstarch for every 2 cups of liquid measured from the slow cooker.
Whisk 2 tbsp cornstarch per 2 cups of liquid measured from the slow cooker with enough cold water to resemble heavy whipping cream, about 1/4 cup of water per 2 tbsp of cornstarch. This mixture is known as a "slurry."
Pour the "slurry" made from the cornstarch and water into the slow cooker while stirring with the whisk.
Continue to whisk the sauce for one to two minutes over high heat or until it reaches the desired consistency.
Turn off the heat or reduce it to low on the slow cooker and serve immediately.
Avoid leaving the sauce over high heat after adding the cornstarch. Excess cooking over a high heat can result in the cornstarch separating from the liquid.