uice the lime and add a cup of water to the juice. (optional)
Place the diced apple pieces into the lime water batch by batch before draining and adding just the apple pieces to the mixing bowl (don't add the lime water).
Add the tuna, parsley, mayo, curry powder, and salt to the mixing bowl.
Mix well. Serve with ricecakes or vegetable sticks.
Put the yolks in a bowl (blender, food processor) with the mustard, if using and 1 tsp lemon juice and mix those ingredients together.
Start whisking vigorously (blender or food processor on low) while dripping the oil very slowly, even drop by drop in the beginning. You're creating an emulsion and if you put too much oil at once, it will separate and will be very hard to save. Whisk non-stop and use a towel under the bowl to help stabilize it. As you add more oil, the emulsion will form and the mayonnaise will start to thicken and you can pour the oil faster at this point.
When all the oil is incorporated and the mayonnaise is thick, add the rest of the lemon juice and taste your creation. You can season to taste with salt and pepper.