While meat is resting, sauté shallot in the fat left in the pan (add a bit of oil if there is no fat)
With the heat on high, pour in your deglazing liquid and stir up all the fond from the bottom of the pan. Reduce by ½ - this will not take long - watch it carefully.
Add the balancing liquid* and reduce until thickened and syrupy.
Taste and adjust seasonings if necessary. You probably won't need salt, but you might want to add some pepper.
Off the heat, swirl in a splash of heavy cream or a bit of butter. This will give your sauce a lovely gloss and rich mouth feel.
Strain (if you want to) and add some minced herbs to finish.