Garlic mustard can be foraged now and throughout the winter as long as the weather is mild and the ground bare. It is edible and frequently abundant, and you need not feel compunction about harvesting as much as you like. Its evergreen tendency probably gives it an aggressive edge in supplanting native herbs.
Indeed, eat away. It’s a major invasive that’s causing trouble in woodlands. New studies sow its roots emit a chemical that makes the soil toxic for many native plants. Plus, I hear it makes a mean pesto!
I’ve steamed it as a spring green and can imagine it would be delicious in pesto. It is practically the only green thing left to forage.