1. Gently combine the steak mince, salt, pepper and Major Roast Onion Stock Base Paste(1) in a bowl.
2. Roll the burger meat into a log shape, wrap with clingfilm and place in the fridge for an hour to set.
3. To prepare the Roast Onion and Bacon Ketchup: Add a splash of oil to a frying pan, heat and fry the onion and bacon until they start to caramelise. Add the cider vinegar, sugar, garlic puree and Major Roast Onion Stock Base Paste. Reduce until the liquid has nearly gone and has become sticky. Season to taste.
4. Onion puree: Place the chopped onions(1) and butter in a pan over a medium heat. Cook with lid on until onions are soft but not coloured. Add the cream, Major Roast Onion Stock Base Paste(2) and blitz in a food processor until smooth. Keep warm.
5. Pickled Onions: Bring the vinegar, water and sugar to the boil in a pan until sugar dissolves. Pour over the onions(2) and leave to steep until cold.
6. Caramelized onions: place the onions(3) in a frying pan with a little oil. Saute for approx 30 minutes on a medium heat. Add Major Roast Onion Stock Base Paste(3) and salt to taste.  
7. Cut the burger log into 20. Flatten each burger slightly.
8. Preheat an oven to 140°c.
9. Take 10 burgers and place 40g of Roquefort on each one then top with the remaining 10 burgers, pressing down to seal.  Return to the fridge to set for 30 minutes. Cook the burgers in the oven for 15 minutes. 
10. Place a griddle on a high heat and toast the brioche buns.
11. Spread the onion puree on the bottom of the buns. Top with lettuce and tomato.
12. Griddle the burgers to finish cooking, then place on top of the tomato. Finish with the caramelized and pickled onions and a serving of onion and bacon ketchup.
13. Top the burgers and serve.