Remove steaks from refrigerator 30 minutes prior to grilling. Preheat grill.
In a medium bowl, toss the sweet potatoes with half of the oil, salt and pepper. Set aside.
Drizzle the remaining oil, salt and pepper on the steaks and set aside while you whisk the glaze together.
Whisk together all the ingredients for the glaze and heat in a small sauce pan over medium low just until the espresso and sugar have dissolved.
Place steaks and sweet potatoes on the grill. Grill steaks for 5 minutes on the first side, brushing occasionally with half of the glaze. Turn over and grill for an additional 4 - 5 minutes, brushing with the remainder of the glaze.
Turn sweet potatoes over when you flip steaks. They are done when a knife easily pierces through them. They will likely be done before the steaks, just keep an eye on them and move them to a cooler section of the grill so they don't burn.