Overview
In English, kasha usually refers to the pseudocereal buckwheat or its culinary preparations. In Eastern European cuisine, kasha can apply to any kind of cooked grain. It can be baked but most often is boiled, either in water or milk, and therefore the term coincides with the English definition of 'porridge', but the word can also refer to the grain before preparation, which corresponds to the definition of 'groats'. This understanding of kasha concerns mainly Belarus, the Czech Republic, Lithuania, Poland, Romania and the Republic of Moldova, Russia, Slovakia, Slovenia, Kazakhstan, and Ukraine, where the term, besides buckwheat, can apply to wheat, barley, oats, millet, rye and even rice. Kashas have been an important element of Slavic diet for at least 1,000 years.
This English-language usage probably originated with Jewish immigrants, as did the form kashi (literally translated as "porridges").
In Ashkenazi Jewish culture
As an Ashkenazi-Jewish comfort food, kasha is often served with onions and brown gravy on top of farfalle, known as kasha varnishkes. Kasha is a popular filling for knishes and is sometimes included in matzah-ball soup.
In Czechia
In Czech the cognate has a wider meaning that also encompasses mashed potato, pease pudding, etc.
From Wikipedia (CC BY-SA 4.0).