Take some potting soil and some spinach seeds. Any container you have is fine as long as it drains. Place dirt in container - sprinkle the spinach seeds - cover the seeds lightly with soil - water - place in a sunny spot.You can cover the container with plastic wrap or a clear cover to keep moist.
In about 7-10 days, you'll see little sprouts. Then the little round leaves will appear a week after. You can start picking the leaves off after that.
Nutrients in the winter - Perfect!