The Familiar by Leigh Bardugo

In a shabby house, on a shabby street, in the new capital of Madrid, Luzia Cotado uses scraps of magic to get through her days of endless toil as a scullion. But when her scheming mistress discovers the lump of a servant cowering in the kitchen is actually hiding a talent for little miracles, she demands Luzia use those gifts to improve the family's social position.

What begins as simple amusement for the nobility takes a perilous turn when Luzia garners the notice of Antonio Pérez, the disgraced secretary to Spain's king. Still reeling from the defeat of his armada, the king is desperate for any advantage in the war against England's heretic queen—and Pérez will stop at nothing to regain the king's favor.

Determined to seize this one chance to better her fortunes, Luzia plunges into a world of seers and alchemists, holy men and hucksters, where the lines between magic, science, and fraud are never certain. But as her notoriety grows, so does the danger that her Jewish blood will doom her to the Inquisition's wrath. She will have to use every bit of her wit and will to survive—even if that means enlisting the help of Guillén Santángel, an embittered immortal familiar whose own secrets could prove deadly for them both.