I use an immersion blender for this, I have never had a great result using a blender.
I call this Primal instead of Paleo because I like the slightly sweet addition of Stevia and I usually use Dijon mustard.
1 large egg + 1 egg yolk
big pinch of sea salt
1 tsp mustard (use what you like)
1 tablespoon lemon juice
1 teaspoon vinegar
stevia to taste
1/2 cup each grapeseed and avocado oil for 1 cup total
(other oils: macadamia oil, olive oil (not all EVOO unless you want a really strong flavor), safflower oil (lots of bad chatter about the omega fat ratio though), add a tablespoon or two of flax oil or hempseed oil, but not too much it’s very strong)
You want to use a mixing cup that is deep and that your immersion blender just fits into without much room. You want all of the ingredients to be in motion.
In the bottom place the egg + yolk, then the mustard, salt, lemon juice, vinegar and stevia. Place the blender down into this then gently pour all of the oil on top.
I aim for the blending head on the blender so it hits that and not the ingredients.
Turn the blender on and let it blend, sitting on the bottom, for 15 seconds, then slowly start bringing it up through the oil.
Once it starts to thicken, move the blender back through the mayonnaise a few times to get it well blended.
If you keep blending, it will break and you can make a lovely LARGE batch of salad dressing instead (add vinegar and water, then re-blend for the dressing).
Keep refrigerated for up to one week.