Place salt rock on a baking pan in a cool oven. Turn oven on and heat to 200 degrees. Let salt sit at 200 degrees for 30 minutes. Increase oven temperature to 450 degrees and let it come to temperature for 45 minutes.
The salt is now ready to cook on. Place the ahi (or another raw fish of your choice) on top and allow cooking until desired doneness.
Let salt cool down and rinse with cool water. Use a brush to remove debris. Dry with towel (the salt can be used many times in hot or cold applications).
Place limes, sugar, garlic, jalapeño, cilantro, mustard and Soy sauce in a blender. Puree all ingredients until smooth. Slowly pour in the lime oil to emulsify.