Prep a large head of cauliflower by removing the core and green leaves. Cut the head of cauliflower into chunks that fit inside a large pot. If you cut the cauliflower into small pieces, it will fall apart in the pot later or get too soft too quickly. Place the cauliflower in your pot and fill with water until the cauliflower is covered. Bring the pot to a boil over high heat and cook the cauliflower until it’s tender enough to pierce through with a fork – 12-15 minutes.
Once the cauliflower is tender, drain the water. Use a pair of tongs or a slotted spoon to transfer the hot cauliflower to a food processor. Let any excess water drip off the cauliflower before piling it up in the food processor. Add in the butter and softened cream cheese while the cauliflower is still hot. Pulse the food processor until the cauliflower is mashed. Then, use the pulse button to mix in the salt and pepper.
Scoop the mashed cauliflower into a large bowl. While the mashed cauliflower is cooling, stir in shredded pepper jack cheese. Make sure the cheese is spread throughout the cauliflower as it melts to help bind the mash as it cools more. Finally, mince and fold in a fresh jalapeno pepper into the mashed cauliflower. For serving, you can top off each portion of mashed cauliflower with thin slices of jalapeno and additional shredded cheese at your discretion.