Spice-Rubbed Steaks with Spinach

1 1/4 teaspoons cayenne pepper
1 teaspoon ground coriander
1 teaspoon ground cumin
1 teaspoon fennel seeds, lightly crushed
1 teaspoon sweet paprika
1/2 teaspoon ground cardamom
Salt and freshly ground pepper
4 Delmonico or boneless rib-eye steaks (about 2 1/4 pounds total), pounded 1/2 inch thick
3 tablespoons unsalted butter
2 tablespoons extra-virgin olive oil
2 large garlic cloves, finely chopped
10 ounces baby spinach

In a small bowl, combine 1 teaspoon of the cayenne pepper with the coriander, cumin, crushed fennel, sweet paprika, cardamom, 1 1/2 teaspoons of salt and 1 1/2 teaspoons of pepper. Sprinkle the spice mixture on both sides of the steaks, patting them onto the meat.
In a large, heavy skillet, melt 2 tablespoons of the unsalted butter in 1 tablespoon of the olive oil. Add the chopped garlic and the remaining 1/4 teaspoon of cayenne pepper and cook the garlic over moderate heat, stirring, for 2 minutes. Add the baby spinach to the skillet and cook, turning, until the spinach is wilted, about 5 minutes. Season the spinach with salt and pepper. Transfer the spinach to a serving platter and keep warm.
Wipe out the skillet and melt the remaining 1 tablespoon of butter in the remaining 1 tablespoon of olive oil. Add the Delmonico steaks to the skillet and cook the steaks over high heat for about 3 minutes per side for medium rare. Set the steaks on the wilted spinach and serve at once.