At its core, a gastrique is a sweet and sour sauce. Usually the sugar source is caramelized to give some extra depth.

The components that actually make it sweet and sour can vary, so it might use fruit, caramel, wine, vinegar, etc

>gastrique

A gastrique is a type of sweet and sour sauce made by reducing sugar and vinegar together, and it is commonly used to add a touch of acidity and sweetness to savory dishes. Some examples of dishes that use gastrique as an ingredient include:

Duck breast with cherry gastrique: This dish features seared duck breast served with a sauce made from reduced cherry juice and red wine vinegar.

Pan-seared scallops with grapefruit gastrique: This dish features scallops seared in butter and served with a sauce made from reduced grapefruit juice and white wine vinegar.

Pork tenderloin with apple gastrique: This dish features pork tenderloin roasted and served with a sauce made from reduced apple juice and apple cider vinegar.

Beef tenderloin with balsamic gastrique: This dish features grilled beef tenderloin served with a sauce made from reduced balsamic vinegar and sugar.

Vegetables with Caramelized Onion Gastrique: This dish features roasted vegetables with a sauce made from caramelized onions and red wine vinegar.

It generally a sauce made from vinegar and sugar will likely have other ingredients added to it. Blueberry gastrique is a very common sauce to serve with duck. I like to make it with blueberries, red wine vinegar, white sugar, brandy, shallots and duck stock.