Trim and thinly slice the spring onions.

Into a frying pan on medium heat, add the honey and cook until it turns a dark amber colour, 2-4 mins. Then take it off the heat and add the rice vinegar, soy sauce, and chilli flakes. Place it back on the heat and cook until sticky and slightly thickened, 3-4 mins.

Cook the udon according to the packaging instructions.

Whisk the cold butter into the burnt honey teriyaki. Then toss the udon into the sauce until glossy and coated. Taste and season with more soy or rice vinegar if needed.

Share the udon into bowls. Garnish with spring onions.