I’ve seen serious gardeners use a casserole dish as a greenhouse to save a struggling plant. Of course, a large mason jar will work even better. Here’s a picture of lettuce seedlings getting a head start on life inside the warm embrace of a former tomato sauce jar.
The biggest problem in using this type of setup is adequate air flow. Like human beings, plants need to breath. A better setup would add a bendy straw under the soil to act as as a tiny plant snorkel. If your plants can’t breath, they can’t grow – and if they don’t grow, you can’t eat them!