or work into
If you work one substance into another or work it in , you add it to the other substance and mix the two together thoroughly.
Gradually pour the liquid into the flour, working it in carefully with a wooden spoon...
Work in the potato and milk until the mixture comes together...
Work the oil gradually into the yolks with a wooden spoon.
PHRASAL VERB : V n P , V P n (not pron) , V n P n