-prepare the avocado dressing
1. Pound the garlic in a mortar and pestle until smooth then add the egg yolk and whisk in the oil to make a stiff aioli. Season with salt and white pepper and add lemon juice to taste.
2. In a blender or food processor, puree the avocado with the buttermilk until smooth. Add the aioli and mix well. Season to taste with salt and white pepper.

-prepare the lemon vinaigrette
1. In a small, nonreactive saucepan, simmer the lemon juice and reduce it by half. Transfer to a small bowl and allow to cool. Add the shallots and herbs then whisk in the oil. Season to taste with salt and white pepper.

-to assemble the dish
1. Drizzle the avocado dressing in a ring around each of four cold plates. Arrange the avocado slices, grapefruit and blood oranges around the outside of each plate alternating slices.
2. Toss the crab claws and legs in the lemon vinaigrette and arrange them around the plates over the sliced avocado and citrus.
3. Toss half of the arugula with a small amount of the lemon vinaigrette and place in the center of the plates.
4. Coarsely chop the remaining arugula and toss with the picked crab meat and the remaining lemon vinaigrette. Place in a small mound in the center of each plate.