The recipe makes almost a focaccia-style bread dough that is then rolled out, filled with a potato & cheddar filling, then baked until golden. It’s perfect on its own, but also as a hearty companion to soup, chili or stew. It's also great slathered with sour cram and a sprinkling of chopped green onions - just like regular pierogies!
1. For the dough, put all of the ingredients in the bowl of a mixer fitted with the dough hook attachment, and mix on low speed until blended, increasing the sped to medium to knead until the dough feels elastic, about 5 minutes. Alternatively, the dough can be mixed by hand, and turned onto a work surface to be kneaded until elastic (7-10 minutes). Place the dough in a bowl, cover and allow to rise until doubled, about an hour.
2. While the dough is rising, prepare the filling. Boil the potatoes in salted water until tender and drain. Use a mixer, beaters or a ricer to mash the potatoes and stir in the butter and cheese. Season to taste and cool to room temperature (this can be prepared a day ahead and chilled).
3. Turn the risen dough out onto lightly floured work surface, divide into 2 pieces and roll out each piece to a large circle, about ½-inch thick. Divide the filling between the 2 pieces of dough and spread it to cover half of the dough in a half-circle shape. Fold the unfilled half over the filling (the bread should now have a giant pierogy shape to it), press out any air pockets and pinch the edges closed. Place the breads onto parchment-lined baking trays, cover each with a tea towel and let rise for 30 minutes.
4. Preheat the oven to 375F (190C). Use a fork to dock the top of the bread a little, and brush with the egg wash. Bake the bread for about 40 minutes, until a golden brown. Cool for at least 15 minutes before slicing to serve.
The bread will keep for up to 2 days, well-wrapped or can be frozen.