Digging. And doing so before they set seed.

Try digging during the winter. You can usually see the rosettes. I would use a very long digger or my favorite a long carving knife to push into the soil and twist. If the root it broken off near the surface it may regrow the top.

Never let any of them flower and produce seed. Get them out regularly. Just one flower can reseed a whole bed.

I have a weeder called a Weed Witch that I use mostly for the prickly thistles. Kinda fun to screw them out of the ground with that. The flame torches look like fun, also, but I don't have one and can't say how it would work on the thistles.