Heat a medium saucepan over medium heat. Add a teaspoon of neutral oil (not listed in ingredients; use a splash if needed). Add the finely minced onion and cook, stirring, until translucent and softened, about 5–6 minutes. Add the minced garlic and cook 30–45 seconds until fragrant, taking care not to brown.

Build the Sauce

Combine base ingredients

Reduce heat to medium-low. Add the ketchup, brown sugar, apple cider vinegar, and molasses to the pan with the aromatics. Stir thoroughly to combine and dissolve the brown sugar.

Add savory seasonings

Stir in the Worcestershire sauce, Dijon mustard, and soy sauce until evenly mixed.

Add spices

Sprinkle in the smoked paprika, chili powder, ground black pepper, salt, and red pepper flakes. Stir to distribute spices, breaking up any clumps of brown sugar or paprika.

Adjust consistency

Pour in the water to thin the sauce to your desired consistency. Stir to combine.

Simmer & Finish

Simmer

Bring the sauce to a gentle simmer, then reduce heat to low. Let simmer, uncovered, stirring occasionally, for 15–25 minutes until slightly reduced and thickened to a glaze-like consistency. Taste midway and adjust seasoning as needed.

Finish for gloss and brightness

If using, stir in the butter until melted for a glossy finish. Add lemon juice a little at a time (up to the listed amount) to brighten the flavor, adjusting to taste.

Cool and store

Remove from heat and let cool to room temperature. Transfer to a clean jar or container and refrigerate. Sauce will keep 2 weeks refrigerated. Rewarm gently before using on grilled meats or as a condiment.