1. Prep the toppings for your salmon first: Halve the cherry tomatoes and toss together with the chopped parsley and capers in a bowl. Season with salt to taste and then store in the refrigerator until you are ready to serve.
2. For the whole grain mustard aioli, blend together the egg, lemon juice, and 1/4 cup of vegetable oil in a blender until the mixture has started to thicken up and turn opaque in color. Once that has begun, slowly pour the remaining 1/2 cup oil into the blender while it is in motion. The mixture should thicken into a more mayonnaise-y consistency. **If it is still loose after adding the remaining 1/2 cup of oil, add a little more oil while it is blending until it does thicken up.
3. Once the mayonnaise has come together, add the whole grain mustard and salt to taste. You want it to be a little runny so you can spoon it over the salmon. If it is too thick, add a couple of splashes of water. Store in an airtight container and keep in the refrigerator.
4. Right before you are ready to eat, season the salmon with salt and pepper and add a little oil to a cast iron skillet before preheating it to medium-high. When the pan is hot enough, place the salmon skin side down first (if no skin, start on either side.)
5. Cook the salmon, placing a lid or a loose piece of foil over the fish to help trap the heat and cook the center of the fish. When the skin is crispy and you can see the side closest to the pan is half way cooked through, flip and let finish cooking. **Remove the lid for the second side because trapped moisture will soften the crust you created on the first cook.
6. When the salmon is finished cooking, remove from the pan and plate. Spoon over some of the mustard aoili and finish with some of the tomato-caper relish. Serve right away.
Tips + Tricks
**If having a good crust on your salmon is not important to you and you would prefer something easier, you can always place the salmon on a parchment-lined cookie sheet and cook at 400 degrees until cooked completely.
**Salmon only needs to be cooked to 145-degrees to be considered safe, which is why we always recommend cooking to your preferred doneness. Ideally, the fish will be firm, but with a little give.