Having grown up in Austin, I love Texas barbecue as well as Tex-Mex.
I make my own Southwestern barbecue sauce, following a few guidelines (I rarely, if ever measure anything when I cook, so bear with me)

Basic ingredients:
- Olive oil, canola oil or butter
- Roasted tomatoes (12 fresh or 1 large can)
- Molasses
- Honey
- Chipotle chilies (dried, canned or ground)
- Garlic
- Shallot or white onion
- Fresh Cilantro
- stone ground mustard
- 1 bottle of good microbrew of choice
- white vinegar
- salt
- chili powder
- fresh ground black pepper
- ground cumin
You'll need a fairly fine sauce strainer and a blender, as well.
I start by mincing a hefty amount of garlic, then coursely chopping another batch for good measure (equivalent of a small handful total, perhaps 15-20 cloves). Then, coursely chop about 2 large yellow onions or 4-5 shallots.
If I'm using dried chilies, I soak 3-4 (or more) dried chipotles in boiling water for about 5 minutes, then I remove the stem and coursely chop them (you can remove the seeds to tone down the heat). Rinse and coursely chop about 5 stalks of cilantro.
In a large skillet or saucepan I saute the garlic and onion in oil or butter, adding the chilies as the onions turn translucent. Then I add about 1 tablespoon of molasses and about 1/2 cup of honey and carmelize the onions/garlic.
At that point I add the roasted tomatoes, cilantro and the beer, bring to a boil, then reduce and simmer (with the lid tipped a little to allow some of the liquid to boil off) until everything is looking saucy (about an hour).
After a brief cooldown, I put the whole shabang into the blender, whip it up a bit, then strain it into a tall saucepan.
Toast about 1/2 tsp cumin in a skillet.
Now for the final seasoning and fine tuning.
With the sauce on a medium simmer, I slowly add mustard, honey (if needed), salt, pepper, cumin (a pinch at a time), and vinegar(if needed) until the sauce hits the perfect point where my whole mouth is blissfully activated by the flavors.
Yes, this is a BIG sauce. I like it basted on chicken with a good hoppy IPA on the side.