Salt the medallions. For better flavor, we recommend salting the medallions about a half hour before you’re going to cook them. However, you could instead salt just before cooking.
Heat the quarter cup of high heat oil to 350˚F in a deep pot.
Dry off the capers thoroughly and fry them in the oil until some of their leaves pop open and they’re crispy. Move them from the oil to paper towels to drain.
Make the Parsley Oil: Put the parsley leaves and oil in a blender and blend until the mixture turns a bright, vibrant green. You don’t need to blend it into a puree.
Pour the mixture from the blender into a fine-mesh strainer set over a bowl. Let the oil drain through at its own pace. Do not press on the solids – doing so can cloud the oil.
Make the Celery Root Puree:
Optional: Cut two slices from the parsley root about 1cm thick. Slice those slices into ½ inch cubes for use as a garnish.
Cut the (remaining) celery root into large chunks, cover with lightly salted water and simmer until very tender (but not falling apart).
Drain off the water, reserving 1/3 cup in a separate dish.
Put the celery root in a blender or food processor. Puree until smooth with the cream and ¼-1/3 cup of the water (however much you need to get the proper consistency).
In a large frying pan combine the butter and rosemary with salt and pepper to taste.
Optional: Add the ½” celery root cubes reserved from the puree process to the butter.
Cook the butter over medium-low heat, stirring occasionally, to brown it.
The butter has browned when it starts to smell nutty and you can see brown specks floating in it when you spread a little on a white surface.
Remove the celery root cubes (if you’re using them) to one bowl & pour out the browned butter into another.
Use a paper towel to clean all the residual butter out of the pan.
Pour the tsp of high heat oil into the pan. Heat the pan over medium-high heat. Sear the Merino just until the bottom side turns brown, then flip the pieces and reduce the heat to medium-low.
When the medallions are almost cooked, add the browned butter to the pan and baste the medallions with it.
When the medallions are cooked the way you like them, remove them from the pan and let them rest (covered).
Add the sherry vinegar to the remaining browned butter in the pan.
If necessary, gently reheat the celery root puree in a pan on the stove.
Serve the medallions atop celery puree, garnished with fried capers, the parsley oil, brown butter sauce and (optionally) the celery root cubes.