Add the soaked cashews, almond milk, and lemon juice to a high-speed blender and blend on high for 2 to 3 minutes, or until smooth and creamy, stopping to scrape down the sides as needed. Transfer the cream to a medium mixing bowl and whisk in the grated horseradish, mustard, vinegar, sea salt, and black pepper. Refrigerate for at least 1 hour to allow the flavors to meld and intensify.

One at a time, carefully stand each head of cauliflower on its stem and use a sharp knife to cut it in half down the center. Then, stand each half on its stem and cut as many ½- to ¾-inch-thick cauliflower “steaks” as possible, moving from the center outward. Repeat with the second head of cauliflower. You’ll want at least 4 cauliflower steaks in total but preferably 6. Place the cauliflower steaks in a large baking dish (it’s okay if they’re overlapping slightly) and reserve the leftover florets for another use.

Prepare the marinade. In a medium mixing bowl, whisk together the olive oil, lemon juice, white wine vinegar, parsley, tahini, garlic, sea salt, and black pepper to taste. Pour the marinade evenly over the cauliflower steaks, spooning excess marinade onto any spots that were missed. Marinate for 30 minutes; spoon the marinade over the cauliflower steaks every 10 minutes to ensure they’re evenly coated.

After about 15 minutes of marinating, preheat the oven to 400˚F and line a large baking tray with parchment paper.

Remove the cauliflower steaks from the marinade and spread them out in a single layer on the lined baking tray. Bake for 30–35 minutes, or until golden brown and tender, gently flipping at the 15-minute mark. Remove from the oven and cool slightly.

Spoon as much of the horseradish sauce as desired over each plate. Top with the cauliflower steaks, and garnish with the capers and a sprinkle of parsley, if desired.