• an ingredients table rather than an ingredients list (i.e. where quantity, unit, and ingredient name are columns; and quantity is right-aligned, like any other numeric column in Excel); with sensible units that don't assume their regional growing conditions or food-product design carry over world-wide — so no "sticks" of butter, no "glugs" of oil (from what spout diameter?), no "drops" of flavorings, no "inches" of ginger, etc. Give me volumes! Weights! Molar concentrations! (Half-kidding on the last one.)
• put all references to an ingredient in the steps in bold, and always use the same name for an ingredient that the ingredients table itself uses.
• no implicit ingredients (yes, put the salt and water that the pasta gets boiled in, into the ingredients! Let me mise en place without reading the steps!) Also, don't say "200g sugar" if you mean "100g sugar for the cake sub-recipe; 100g sugar for the frosting sub-recipe." Break those out, so that the fact that those separate quantities should be kept separate is explicit, rather than something you must implicitly gather from the steps.
• or go further and make the ingredients table into its own kind of "pre-recipe" — a sequence of preparation steps. Not only "measuring things into bowls", but also steps such as: explicitly buying things day-of if they're best fresh; or defrosting, if the ingredient is often kept frozen (with defrosting times added to the total amount of time the recipe takes!); etc. Write down exactly what a chef would train their prep cooks to do for them in the preparation phase of this recipe.
• a print stylesheet that makes the webpage come out as a single compact printed page, with a big title, large text, a small picture of the finished product, and no dead space or colored backgrounds (or alternately, a link to a single-page pre-generated PDF with even-more exacting formatting.) I don't want my iPad (that keeps going to sleep and must be woken up with dirty fingers, and can get splattered by oil) in the kitchen; I want to print recipes and put them in transparent binder sleeves. Give me recipe pages I can both easily flip through, and easily find. Let me build a quality printed cookbook, one page at a time, out of my favourite selected recipes from your site.
• a universal "set serving size" client-side Javascript adjuster, which not only manipulates the ingredients but also the correct timings for steps that depend on weights (e.g. defrosting, searing.) None of this "until 165C internally" nonsense; I always buy the same cuts of meat, so calculate the time required for my food to come to temperature, and then tell it to me. Maybe also insert the adjusted amount of the ingredient being used into the text of the steps, so it actually says "add the milk (1tbsp)" rather than just "add the milk." (The ingredients list is for shopping/prep-phase; I should be able to cook without referring to it!)
• each ingredient name in the ingredients table should have a side-link to a page that talks about substitutes for that ingredient, and how to adjust recipes for that substitution. Ingredients with common substitutes should offer an adjustor select-box right there in the ingredients table, where tweaking it changes the recipe appropriately. (Which means the recipe can now include things that are highly-dependent, e.g. it can ask you what pasta you're using, and then embed in the steps the correct cooking time for that type of pasta; and since the recipe knows what kind of recipe it is, it can specify the al-dente time target if it's baked pasta, or the fully-cooked time target if it's a pasta salad.)
• When a recipe is actually just an arbitrary linearization of a few concurrent sub-recipes (e.g. a dish to cook, and a sauce you prepare and then pour over it right before serving), make this clear. Draw boxes around the sub-recipes' steps, and number those boxes. Then put a little boxes-and-arrows workflow diagram for how the numbered sub-recipes relate to each-other at the top of the steps. Represent each sub-recipe in the diagram as a box with a height proportional to how long its steps take—such that you can eyeball which sub-recipe you'll be done with first. Label the boxes with timers that should be set at the beginning of them (because almost always the end of a box is "take off heat" or "take out of oven.")
I'd bookmark a site like that directly, and use it religiously in preference to any other recipe provider.