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1
Place the meat in a large bowl and add the onion, celery, ketchup, horseradish, Worcestershire sauce and parsley.
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2
Season with salt and pepper.
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3
Mix well but do not overwork, then chill for 1 hour.
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4
While the burgers are chilling, prepare the celeriac waldorf.
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5
Cut the celeriac and apple into small matchstick size pieces, either by hand or with a kitchen mandolin.
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6
Place in a bowl, add the creme fraiche, mustard and raisins; mix well and season with salt and pepper to taste.
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7
Make the Tabasco-cumin ketchup by heating the oil in a heavy based pan, adding the onions and garlic then cooking for 5-6 minutes until softened, but with no colour.
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8
Add all the remaining ingredients except for the lime juice and bring to the boil.
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9
Reduce the heat to low and simmer for around an hour and a quarter, stirring frequently.
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10
Pass the ketchup through a medium sieve, strainer or food mill and return to the pan.
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11
Cook over a low heat for a further 30 minutes or so until the sauce is reduced and thickened in consistency.
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12
Allow to cool before stirring in the lime juice and Tabasco to taste, then refrigerate until needed.
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13
The ketchup can be kept in the fridge for up to 5 days, and longer in a sterilised jar.
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14
Divide the burger mixture into 4 evenly sized patties and brush liberally with oil.
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15
Heat a chargrill or pan grill until hot, add the patties and cook for 56 minutes.
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16
Toast the buns, top with a handful of shredded Cos gem lettuce followed by a heap of celeriac Waldorf.
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17
Place a burger on the bottom half of the bun, drizzle over some Tabascocumin ketchup, then close the bun.
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18
Serve with some extra ketchup and fries.