Kasha Knishes

Name: Kasha Knishes
Cook time: 2 h 25 min
Total time: 2 h 25 min
Cuisine: Asian, Middle Eastern, Israeli
Ingredients: 1½ cups dry whole kasha groats (toasted buckwheat); 1½ medium yellow onion, diced; 2 teaspoons olive oil; 2 tablespoons butter; 2 Yukon Gold potatoes, peeled and cut into 1-inch pieces; 2 ¾ cups all-purpose flour; 1 teaspoon salt; 1 teaspoon baking powder; 1½ teaspoon apple cider vinegar; 1 large egg, beaten; ½ cup canola oil; ½ cup tepid water; 1 egg, lightly beaten, for egg wash