Crack an egg into your immersion blender container. Don’t even bother to separate the yolk. Add two teaspoons of dijon mustard, a tablespoon of lemon juice, and a pinch of salt. Pour in 200ml of oil. I’m using canola because I’m being both cheap and lazy; if you’re neither of these things, spend some time researching the various olive oils and making tasting notes. Put hand blender to the very bottom of the container and blend until it thickens into mayonnaise.