Match your use-case: for sandwich spread or creamy dressing, pick Dijon or whole-grain; for cooked sauces, use mustard powder paste or Dijon.
Start with the listed ratio (e.g., 1:1), then adjust after a quick taste: add a pinch of sugar to round sharpness, or a splash of water/vinegar to loosen.
If your substitute looks too coarse, whisk it smooth or strain briefly for a yellow-mustard-like texture.
If it tastes “flat,” boost tang with a tiny squeeze of lemon or a few drops of vinegar—then re-check sweetness.
Let dressings sit 5 minutes so the mustard flavor emulsifies before final tasting.