1) Cut potatoes lengthwise in 1/2cm squares. Soak cut potatoes in water for 1 hr to remove starch. Heat oil to 163C and blanch potatoes for 5 mins until very soft but not brown. Remove from oil. Drain on paper towels.
2) In a medium saute pan over medium heat, cook bacon until just crisp, taking care not to overcook. Drain on paper towels.
3) In a 2L saucepan, melt butter over medium heat. Add onion and cook about 2 mins. Add garlic and flour, whisk until smooth. Cook 2 mins more. Add chilli sauce and mustard, and slowly whisk in double cream. When mixture begins to simmer, add cheeses and remove from heat. Taste sauce for seasoning. If sauce is too thick, thin with more cream. If too thin, thicken with a little more cheese.
4) Increase oil temperature to 190C. Fry potatoes a second time until crisp and golden brown. Remove from oil and drain again, season with salt immediately. On a large plate, arrange chips in the centre, drizzle with sauce, top with crumbled bacon and chives. Serve immediately.