I normally make mayo in a mason jar with an immersion blender and have never had a batch fail before. I had three batches not thicken up on Monday and yesterday I was able to save a failed batch by adding 2 additional egg yolks. The recipe I am using calls for 1 whole egg, 2 TBSP lemon juice, 1/2 tsp mustard, 1/2 tsp salt, and 1-1/4 cup oil; all at room temp. I put the ingredients in a wide mouth quart mason jar and let them sit for about a minute to let the oil separate out and then blend with an immersion blender without moving the blender. The only thing I've changed is to go from an extra large egg to a large egg. Should I add an extra egg or an egg yolk if I'm using a smaller egg? Or is there something else I'm missing.