Combine the flour, chili powder, cumin, garlic powder, oregano, salt, and optional cinnamon in a small bowl, and set the tomato paste and broth near the stove. The sauce cooks quickly once the pot is hot, so having everything ready keeps the roux from overcooking.

Heat the olive oil in a medium pot over medium heat until a small pinch of the flour mixture sizzles when it hits the oil. This usually takes a couple of minutes, and the oil should look hot and fluid but not smoky.

Whisk the flour and spice mixture into the hot oil and cook for about 1 minute, then whisk in the tomato paste. The mixture should smell nutty and warm, and the color will darken slightly as the flour cooks and the spices bloom.

Pour in the vegetable broth gradually while whisking constantly until the sauce looks smooth and fully combined. If you add the liquid slowly, the whisk should move through a lump-free sauce with no dry pockets clinging to the pot.

Bring the sauce to a simmer over medium-high heat, then lower the heat as needed and cook for 5 to 7 minutes, whisking often. It is ready when the color looks deeper and a spoon or whisk leaves a brief trail with a little resistance on the bottom of the pot.

Take the pot off the heat and whisk in the vinegar, then season with black pepper and more salt if needed. The finished sauce should taste bright, rich, and smooth, and it will thicken a bit more as it cools.