For the sauce, add cold eggs to a saucepan with hot water from the tap, cover and bring to the boil, then remove the lid and reduce the heat to a gentle boil, with total cooking time of 8 minutes. Cool in cold water and peel. The yolks should have firmed up while retaining a jammy texture. Chop roughly.
Meanwhile, heat the butter and 50ml oil in a small saucepan, then add the leek and garlic, cooking over a low heat to soften (about 20 minutes). Add the curry powder and stir through for 30 seconds; remove from the heat.
Add the leek and garlic to a blender or food processor with the eggs, mayonnaise, remaining 100ml of oil, sugar and salt and blend until smooth. Add the vinegar and blend.
Cook the cauliflower in boiling salted water for 6 minutes, then drain and cool on a towel. Once cool, cut into 2cm slices. Cut each slice in half, discarding any woody stem.
Set up a station for crumbing, with flour in one bowl, beaten eggs in another and the breadcrumbs and sesame seeds combined in a third.
Flour the cauliflower, then coat in the egg, draining off any excess. Crumb with the sesame seed mix and set aside.
Heat about 10cm of oil in a saucepan until about 170C. Fry the cauliflower in batches until golden all over (about 3 minutes). Drain on a paper towel and season with salt flakes.
To serve, dollop a spoonful of sauce on each plate and top with cauliflower, adding a lemon cheek on the side.