Potato and buckwheat knysh

Ingredients:

For the test:

• 1.5 cups of wheat flour, plus a little more for working with the dough
• 3 tbsp olive oil, plus more for greasing
• Salt
• 1/4 cup plus 2 tablespoons cold sparkling water
• 2 teaspoons apple cider vinegar

For the filling:

• 700 g peeled and quartered Russet potatoes
• 1 cup buckwheat groats, whole grains or large grains
• 4 tbsp. l. olive oil
• 700 g diced onions
• 1 crushed clove of garlic
• Salt and ground black pepper
• Hot mustard for serving

Preparation:

1. Get started with step-by-step instructions for making knishes

   
   Prepare the dough: Place the flour in a food processor, pulse it, and pour the olive oil through the hole in the lid. Scrape the mixture down the sides of the food processor bowl and pulse again.
   
   In a liquid measuring cup, dissolve a teaspoon of salt in the club soda and vinegar. Pulse while pouring the liquid through the hole in the lid for 20-30 seconds. Turn the dough out onto a floured surface and knead until smooth. Form it into a flat disk, wrap it in plastic wrap, and refrigerate for at least 2 hours.
2. Prepare the filling: Place the potatoes in a saucepan, cover with water, and season with salt. Simmer until tender, 20-30 minutes. Drain and mash the potatoes in a large bowl until smooth.
   
   Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add the onion, garlic, and 1 teaspoon salt. Cover and cook for 5 minutes. Remove the lid and cook, stirring occasionally, until the mixture is golden brown, another 15-20 minutes.
3. Meanwhile, combine the remaining 2 tablespoons of olive oil and buckwheat in a small saucepan over medium-high heat and toast for about 4 minutes. Add 1 3/4 cups of water and a teaspoon of salt. Reduce the heat to medium, cover, and simmer until the water is absorbed, about 10 minutes. Season with salt and pepper. Cool slightly, then add to the bowl with the potatoes. Add the onion and mash.
4. Remove the dough from the refrigerator 30 minutes before making the knishes. Preheat the oven to 190°C and lightly grease a baking sheet with olive oil.
   
   Prepare the knishes by placing them on a baking sheet, 5 cm apart. Bake for 30 minutes, brush with olive oil, and continue baking until golden brown, another 25-35 minutes. Serve with mustard.