From: Epicurious.com
Heat the oil in a frying pan and sweat the onion until soft 4-5 minutes.
Add the garlic and cook until you can smell it. Don't overcook the garlic.
Grate the zest from the lemon and squeeze the juice from 1/2 of the lemon.
Add the lemon zest, lemon juice, sugar, vinegar, ketchup, Worcestershire sauce, hot sauce and chili powder to the pan. Simmer gently 5 minutes.
Adjust seasoning to taste and let cool.
Turn off the heat. Reserve 1/2 of the sauce to serve at the table for dipping.
Light 2 burners on a gas grill. Allow grates to warm then clean the grates with grill brush and wipe clean.
Set 1 burner to lowest flame possible and turn the other burner off.
Brush the tenderloins with cooled barbecue sauce.
Grill over the low heat burner basting every 5 to 7 Mins. Turn the meat after each basting. Keep it wet at all times.
Continue grilling and basting for about 1 hour.
As the meat cooks, you may have to move it further away from the active burner to allow slower cooking over indirect heat.
Be patient and keep the heat low. You'll be glad you did!
Let rest for 5 mins before slicing.
We love this with our dill pasta salad as a summertime meal.
The BBQ sauce keeps well in the frig.
4 servings