All the flavours of a classic burger, packaged neatly in a steamed bun, these are great served with spiralized fries.
Make the dough. Place the flour, sugar, yeast, baking powder, oil and salt into the bowl of a stand mixer fitted with the dough hook. Mix on slow speed, gradually adding the water to make a soft, smooth dough. Remove the bowl from the mixer and cover it with cling film. Leave the dough to rise in a warm place for 30–60 minutes, until doubled in size.
While the dough is rising, prepare the filling. Place the mince, onion granules and garlic powder in a mixing bowl, season with salt and pepper and mix to combine. Divide the mixture into 8 portions and press each portion into the cookie cutter to make patties, each about 1cm deep and 5cm across. Cover and set aside.
Once the dough has doubled in size, turn it out onto a lightly flour-dusted work surface. Using your hands, roll out the dough into a log and divide it into 10 equal-sized pieces (each about 50g). Roll each piece into a ball, lightly dust with flour and place each onto a square of baking paper. Cover the dough balls with oiled cling film and leave to prove for 10 minutes, until puffy.
Once the dough balls are ready, knead one bun with green colouring to an even colour and another with red and leave the remaining 8 buns white. Roll the red and green buns each out into a rectangle and cut into thin strips about 5mm wide. Cover with oiled cling film ready for assembly.
Slice the onion into rings and press out the smallest ones to use (save the larger ones for use another time). Heat the vegetable oil in a large frying pan over a medium heat until hot. Add the onion and fry for about 2–3 minutes, until starting to brown at the edges. Scoop out using a spatula and set aside to drain on a piece of kitchen paper.
Using the cutter, cut out 2 circles of bacon from each rasher and fry in the same pan for about 3 minutes, until crisp. Set aside to drain on kitchen paper.
Using the cutter again, cut out 2 circles from each cheese slice.
Place the sundried tomatoes and cornichons into a small food processor and blitz to a chunky paste.
Using your hands, press one bun at a time into a disc about 9cm in diameter, leaving a slight dome of dough in the middle.
Place ½ teaspoon of the cornichon mixture on the dome of the bun, followed by an onion ring, then patty, then cheese and then bacon. Bring the sides of the dough up over the filling, pinching and sealing the bun over the top of the filling.
Place the bun, seam-side downwards, back on its piece of baking paper, lightly brush with milk, then wrap a green then red strip of dough around the base and sprinkle the top with sesame seeds. Repeat for the remaining 7 balls of dough. Cover with oiled cling film and leave the filled buns to prove for a further 15 minutes, until puffy and risen by one third.
Fill a pan one third full with water and bring to the boil. Depending on the size of your steamer basket, place 1 to 3 buns at a time inside, allowing room for them to double in size. (If you have a two-tiered bamboo steamer, you may be able to steam the buns in one go.) Place the steamer basket on the pan, cover with a tight-fitting lid and steam for 15 minutes, until cooked through. Repeat for the remaining buns.