Smash-style burger on homemade potato buns

Cut eight ounces of russet potato into one inch pieces.

Cover the potato with a little water and boil about 15 minutes, well past al dente, until a fork pushed in breaks the pieces apart easily.

Lift the potato out and keep the cooking water simmering.

Put the reserved half cup of bread flour in the stand mixer bowl.

Measure half a cup of the just-off-boiling potato water over the flour and stir and mash it to a paste, scalding the flour so it absorbs the liquid.

Mash the potato with a fork to break up lumps and let both the paste and the potato cool, so the yeast does not take off and ferment too fast.

Add the mashed potato, two eggs, the oil, the milk, the granulated sugar, 10 grams of salt, the remaining three cups of bread flour and the instant yeast, everything at room temperature.

Mix on low, a long slow mix, until the dough is developed and has structure; the dough stays generally soft and slightly sticky.

If it sticks badly to the bowl, scrape down and add a couple of tablespoons of flour around the sides so the dough pulls it in, then mix another five minutes on low.

Turn out onto a floured surface and gather the rough edges to the centre to form a ball.

Cover in a clean bowl and cold ferment in the fridge, up to 24 hours, until about doubled.

Turn the risen dough out onto a lightly floured surface.

Divide into 12 pieces of a little over three ounces each.

Gather and squeeze the rough margins of each piece together, set it seam side down and roll it against the surface into a tight even ball; keep the flour light so there is tension against the surface.

Arrange the balls on a parchment-lined sheet tray in a four by three grid.

Pat each one flat to about a three inch diameter, or use a little rolling pin.

Heat the oven to 350F.

Tent a proofing bag over the sheet, folding the plastic under to seal, and proof about 45 minutes until very puffy and full of air.

Mix the special sauce: one part ketchup, one part mayo, about half as much mustard, hot sauce, a pinch of garlic powder, salt and the juice from relish; no black pepper.

Slice the onion into thin whole rounds.

Beat the egg yolk with a splash of heavy cream for the egg wash.

When the buns wobble as a unit and show big bubbles under the surface, they are proofed.

Coat each bun with the egg wash, thinned with a little water so it spreads without dragging on the delicate surface.

Scatter sesame seeds over and bake at 350F for about 20 to 25 minutes until well risen and deep golden brown all over.

Preheat the griddle over medium high and turn the hood on high.

Griddle the patties with no added grease; they fry in their own fat, pressed with a burger press for contact.

Cook most of the way on the first side, until the edges crisp and juices pool in the centre of the patty, then flip.

Put the cheese on top and griddle the buttered buns at the same time.

Spread special sauce on both cut sides, then patty, pickles, onion rounds and the top bun.

Serve with a side of ketchup for dipping.