Add the potatoes to a pot of cold salted water and bring to a boil. Lightly boil for 10-12 minutes (depending on the size of the potatoes) or until the potatoes are fork tender.
Drain and mash with the butter, salt, and pepper.
Shred the cheese if needed.
For the Dough
Add the flour and salt to the bowl of a stand mixer and mix well.
In a small mixing bowl, whisk the warm water and sugar together. Sprinkle the yeast and stir. Let it proof for about 5 minutes, or until the yeast is foamy.
Add the yeast mixture to the flour, as well as the egg and melted butter. Mix on low until combined and then turn to medium for 3-4 minutes, until you have a soft and smooth dough.
Lightly flour the counter.
Roll the dough into a circle, roughly 12 to 14 inches wide.
Add the potatoes to the center of the dough, spreading it out but keeping it about 4 inches from the edges. Sprinkle the cheese on top.
Fold the dough over the filling so it’s sealed. Push down to keep it closed.
Flip it over and roll it out to about an inch thick.
Place the filled dough on a baking tray. Cover and let rise for about 30-45 minutes.
Preheat the oven to 400°F (200°C).
To shape the dough, run your fingers around the edge of the dough, about an inch in, to make a circular indent all the way around the dough.
Next, with your fingers pressed tightly together, indent lines in the dough about an inch and a half apart, staying inside the circular indent. Press diagonal lines going the other way as well, so you end up with diamond shapes.
Brush the dough with the egg wash.
Sprinkle with nigella seeds and sesame seeds.
Bake for 30-40 minutes, or until the dough is cooked and golden brown.
Notes
Store leftover bread tightly wrapped at room temperature for up to 2 days, or refrigerate for 3-4 days.Weighing flour is the most accurate. I use Costco all-purpose flour. You may need a little less flour if you're measuring instead of weighing. Read why flour weighing flour is the most accurate.