Place the eggs back into steamer basket and back into Instant Pot/pressure cooker. Rest the lid on the pot, so that the eggs will continue cooking from the residual steam in the pressure cooker. Let eggs sit in pot for 5 minutes.
In a medium bowl, mix together mayonnaise, Dijon mustard, yellow mustard, celery, minced pickles (or relish) and pickle juice.
Add salt and pepper and mix through. Taste and make sure the dressing is a bit saltier than you like, so that when the cauliflower and eggs are added, the salad will be perfectly seasoned. If it tastes perfect, add more salt.
Chop scallions and set aside a handful of the green part for garnishing the salad.
Mix in horseradish sauce and the rest of the chopped scallions.
Spoon dressing into the bowl of warm cauliflower and gently and carefully mix the dressing with the cauliflower to combine. Be careful not to smash the cauliflower. If there are still large chunks of cauliflower, use the spoon and cut them into bite size pieces.
Remove eggs from pressure cooker and run them under cool water.
Peel eggs under the water, making sure that all the eggshell is removed.
To dice the eggs, use a baking rack (see video) and place one egg at a time onto rack. Using the palm of your hand smash down on the egg so that the egg will fall through the grate on the rack and into the bowl. For any egg stuck to the rack, use your fingers and rub over the egg, which will cause the rest of the egg to fall through the grate into the bowl.
Alternatively, a knife or an egg slicer can be used to chop the eggs.
Very gently, combine eggs with the cauliflower and dressing.
Cover bowl with cellophane or other covering and place into refrigerator overnight, or until very cold (about four hours). As the cauliflower cools and absorbs the dressing, it will also swell and firm up.
Place cauliflower salad into a serving dish.
Garnish with paprika and the reserved green parts of the scallions.
Regarding the eggs. Use as many as you like in your mock potato salad. My head of cauliflower weighed 26 ounces and I used four eggs. For me, that is a good amount. Some people may prefer not to add any eggs at all and that is fine. If that is the case, just reduce the amount of the salad dressing or use a larger cauliflower. Different brands of pressure cookers have different PSI, so some pressure cookers will cook the cauliflower at a higher PSI and others at a lower PSI. Therefore depending on your brand, you may need only a "0" minute cook time or a 1 minute cook time. Remember, that while the pressure cooker is coming up to pressure and then when the pressure is releasing, the cauliflower will continue to cook. Cauliflower is a food that cooks super fast and is very easy to over cook. Most pressure cookers will only need a "0" minute cook time.