Ranunculus ficaria (lesser celandine). I'm also dealing with it
I went out after it rained and pulled as much as I could, but it's a daunting task and doesn't pull very easily. I found that loosening the soil around the plants helped get the roots in areas where I had a few scattered plants but didn't have any luck with the giant clusters like in your photos. I also recently posted for help getting rid of these guys so I'll be curious to see if anyone has any good ideas!