ugniatać in English:

i knead the dough

: to prepare (dough) by pressing a mixture of flour, water, etc., with your hands to manipulate or massage with a kneading motion <kneaded sore neck muscles>

Knead the dough with both hands until it becomes elastic.

Unblended gold in its pure form is so soft, that one can knead it by hand.

which do you prefer, mashed potatoes or jacket potatoes

mashed potatoes, mashed peas