Last year, Djokovic's nutritionist discovered that Djokovic is allergic to the protein, which is found in common flours.

WSJ: Novak Djokovic's Gluten-Free Ascendancy

At Tartine Bakery and Bar Tartine, both in San Francisco, Chad Robertson uses buckwheat flour in combination with other flours in many of his breads.

WSJ: Buck-Wild for Buckwheat

Determined to keep the pura vida alive in New York, I tried using different cheeses, flours and oils, but over time my empanadas got worse and worse reflecting, in some ways, the distance that was growing between Costa Rica and me.

WSJ: Jessica Soffer on a Costa Rican Empanada Recipe