• 1 1/2 tsp. freshly ground black pepper
In a medium saucepan, combine the vinegar, onion, garlic, chipotle pepper, bourbon, coriander and paprika. Bring to a gentle boil over medium-high heat, then reduce the heat to medium-low and simmer until the flavors come together, about 10 minutes.
Meanwhile, in a medium bowl, whisk together the 1 tablespoon chipotle purée, brown and yellow mustards, maple syrup, soy sauce, salt and pepper. Strain the vinegar mixture through a fine-mesh sieve into the mustard mixture (discard the solids) and whisk until smooth and combined. Use immediately or store in the refrigerator in an airtight container for up to 1 month.
Note: Large cauliflower forms dense heads that make fun "steaks" for grilling. They take to all sorts of seasonings and accompaniments, so it's easy to build a satisfying meal around them. From "How to Grill Everything," by Mark Bittman.