Butter Cup Take Over
What this looks like is lesser celandine https://en.wikipedia.org/wiki/Ficaria_verna This is considered a noxious weed by the City of Portland https://www.portlandoregon.gov/bes/article/433193. The recommended course of action is a combination of herbicide (e.g. glyphosate, the active ingredient in Roundup) and manual removal. It is important that you do not put what ever you pull up or cut in your yard debris--put it in your trash. If the plant has already formed a thick mat and there are no plants you need to protect, you could also try black plastic to prevent the plant from photosynthesizing. This will certainly weaken the plants and it may take several years to completely eradicate it. Other ideas are to cut off the leaves and blooms now so it cannot go to seed and the leaves cannot feed the bulbs. If the plant pushes up more leaves, simply keep cutting them back.
I wish I could give you a 'silver bullet' but there isn't one at this time.