Identify the product first
Fresh chillies, dried flakes, powder and prepared sauces differ considerably. Even similar-looking peppers can have different heat levels. Read the name, ingredients and dosing instructions. A familiar mild product is easier to judge than an unknown mixture; highly concentrated extracts are not ordinary substitutes for chilli flakes.
Do not transfer quantities unchanged from fresh to dried chilli or from one brand to another. When a dish works well, note the product and amount used. Next time, a little less can then mean less of the same ingredient. Include the number of portions and amount of sauce in that note too.
Season in small stages
With an unfamiliar product, start well below the usual quantity of a familiar one and keep the rest back. Add the chilli to the sauce according to the recipe, mix thoroughly and taste a small sample that has cooled slightly. Do not add more immediately after every bite; allow time to assess the effect.
In a garlic-and-oil sauce, neither the chilli nor the garlic should burn. Tomato sauce provides more liquid for distributing the seasoning, but still needs thorough stirring. If only one serving should be hotter, separate that portion of the finished mild sauce and season it independently. The other plates can then stay as they are.
Prepare fresh peppers carefully
Wash the chilli and remove the stalk. Removing the pale inner parts along with the attached seeds can reduce the heat, but does not reliably make a hot variety mild. Cut the amount you intend to use finely enough to avoid concentrating large pieces in a few bites. Distributing an unfamiliar extremely hot pepper carefully does not make it a suitable everyday ingredient.
Wear suitable gloves when handling hot chillies and avoid touching your eyes. Clean your hands, knife and board afterwards. For a group with different preferences, a mild base sauce and a familiar, clearly identified chilli seasoning for individual use are usually more practical than making the whole batch strongly spicy from the outset.
Dilute an over-seasoned sauce with a matching base
If the sauce is unpleasantly hot, increase its quantity with a compatible sauce base containing no chilli. For tomato sauce, that could mean a separately fully cooked tomato base. Adjust the salt and consistency afterwards. More sauce also means more servings or a revised storage plan, and the amount of pasta should still make sense alongside it.
Sugar, lemon juice or a piece of potato do not reliably remove the chilli. Cream or cheese change the flavour and recipe rather than providing a universal solution. If a small sample remains unpleasant after dilution, serve a different sauce. Next time, holding back some of the chilli will help more than trying to extract heat that has already been mixed in.