Pan-Braised Radishes And Greens

Trim the greens from the radishes, leaving a bit of the green stem intact. Place greens and radishes in a large bowl of cold water and let soak for at least five minutes. Remove greens and set in a colander to drain. Dry off radishes and slice in half. Note: Quarter larger radishes; leave small ones whole.
Mince the shallot. In a large saute pan, melt three teaspoons of the butter and sweat the minced shallots over medium heat for a minute or so -- you don't need any color here. Add radishes to the pan and season with a pinch of salt and pepper. Pour in water to almost cover the radishes -- the top surfaces should be peeking out a bit. Bring to a simmer, partially cover the pan, and cook until the radishes are knife tender, about 5 to 8 minutes depending on the size of the radishes. Remove the lid and add the greens to the pan. Cover and cook for a minute or two more, until the greens have somewhat wilted. Use tongs to stir them a bit. Transfer greens and radishes to a large mixing bowl leaving juices remaining in pan.
Bring juices to a simmer, and reduce until no more than a quarter cup remains. Add a teaspoon more of butter and stir to incorporate it with the juices.
Finely chop the tarragon and add it to the bowl. Pour reduced juices overtop and toss to coat. Taste. Add more salt and pepper if necessary. Add just the smallest sprinkling of vinegar for a touch of brightness if necessary. Transfer greens and radishes to serving platter.