Step 1

Melt butter in a small saucepan over medium heat. Add onions, sauté 4 minutes, add tomato paste and sauté 2 more minutes.

Step 2

Stir in water, apple cider vinegar, sherry vinegar, Worcestershire, mustard and tamarind; bring to a boil and continue at medium heat for one minute. Reduce heat to low, add dates and simmer 10 minutes.

Step 3

Remove from heat and purée until smooth with an immersion blender or tabletop blender. Note: if using a traditional tabletop blender, remove the filler cap from the lid and cover with a tea towel (this will allow some steam to escape without the lid popping off). Keep sauce warm.

Step 4

Season T-bone steaks with salt and pepper; grill to desired doneness (suggested 125-130° F internal temperature for medium rare). Rest 5 minutes tented with foil; serve with sauce.