Recipe: Potato Bok Choy Gratin

My husband and I belong to a CSA (community supported agriculture) cooperative.  The farm we support is Snow's Bend Farm outside of Tuscaloosa, Alabama.  In this part of the country, at this time of the year, we start getting huge volumes of cold-weather crops like chard, kale, turnips, and sometimes even more exotic items like kohlrabi.  After a while, our kitchen is covered in green.

One of the things we have been getting in large quantities this month is bok choy.  I decided our refrigerator had too much bok choy, so I made this gratin.  Here's the recipe:

Bok Choy Potato Gratin
Dutch oven
8" cast iron skillet
chef's knife or cleaver
paring knife

6-8 large red skinned or other waxy potatoes
1 head of bok choy (about 1 pound), diced
1 sweet white onion, diced
3 T unsalted butter (1 T for cooking the bok choy and 2 T for a béchamel)
2 T unbleached all purpose wheat flour
2 oz. each of 3 types of cheese (I used Havarti, chèvre, and Parmesan)
whole milk (enough to fill the space remaining in the skillet, about 1.5 cups)

Par cook the potatoes by boiling them whole in a Dutch oven with enough water to cover.  Remove the potatoes to cool.  Slice into 1/8" slices and set aside.

In the cast iron skillet, sauté the bok choy and onion in 1 T butter until onion is transparent.  Turn down to medium and cook until caramelized.  Remove and set aside.

Use <1 tsp of water to deglaze the skillet and turn back up to high.  Melt 2 T of butter and add the flour.  Once the flour is browned, add water and/or milk as desired to make a roux.  Set aside (I usually just pour it into a teacup or measuring cup).

Preheat an oven to 400F.  In the cast iron skillet, layer potatoes, bok choy mixture, cubed cheese, and béchamel until all ingredients have been used.  Fill the skillet up to within 1/4" of the rim with whole milk and place in the oven.  Cook until heated through and browned on top, about 40 minutes.