Place the eggs, mustard, vinegar, a little salt and pepper into a Thermomix or blender and process until reasonably smooth.
Meanwhile heat the butter until melted and cook until the butter starts to boil and rise, reduce the heat and swirl the pan to avoid the butter boiling over. Cook until the colour is dark amber and you can see specks of brown fat solids.
Allow to cool to hand hot, pour into a jug with all the nutty solids.
With the blender running, slowly add the melted butter as you would for mayonnaise, scrape the bowl down from time to time. Check seasoning and add a little lemon juice as required.
