Sauteed chicken breast with lemon caper sauce w/ potato-celeriac puree

In The Best Recipe, Cooks Illustrated stresses that lightly floured chicken breasts should be sauteed at high heat so they brown on the outside and cook through to the middle.  That's sage advice that I've learned to follow over time.

The lemon caper sauce is simply a reduction of sauteed scallions, chicken stock, lemon juice, and capers, with butter stirred in off heat.  It's important to reduce this sauce quite a bit, because the butter only thickens it so much.

I served the chicken with a celeriac and potato puree, following the recipe in Chez Panisse Vegetables.  Celeriac isn't one of my favorite vegetables.  Alice Waters' advice to flavor it with white wine vinegar substantially improves the taste.  Vinegar and salt are essential to balance the strong vegetal flavor of the celeriac.