Depending on era and location, some modifiers that could come into play would include:
- equipment availability and quality of that equipment (for example, a fully stocked, professional-grade kitchen vs. typical college apartment equipment)
- cookbook(s)
- experienced assistant(s) or tutor(s)
- familiarity with the kitchen (the first time in a new kitchen, just finding all the things is tricky)
- well-stocked larder/pantry/fridge/freezer
- high-quality ingredients (fresh seasonings instead of dried powders, or higher-quality cuts of meat instead of cheaper cuts, etc.)
- time (a rushed meal is more likely to have flaws than one where the cook has time to plan it out and do things in the right order)
- complexity of the dish(es) (pizza or spaghetti and sauce is easy. But a 3 or 4 course French dinner? That's going to be a higher challenge rating)
- the person/people eating the food (I can cook a darn good pot of chili. But if the consumer is a professional chili cook-off winner, s/he's going to think my chili is crap. A professional taster or chef will be more aware of even the tiniest flaw than the average diner)
- familiarity with the recipe. (Someone who is an expert on preparing Japanese cuisine would get a bonus on preparing Japanese food, and possibly a bonus on some other similar Asian dishes. But wouldn't necessarily get any bonuses on preparing Mexican food...)
- Training on equipment available. (Stick me in a true, professional-grade kitchen and I would be lost... And any trained chef of today would likely be hard pressed to master cooking in medieval Europe's standard kitchens)
- practice (Cooking in general; okay that's a skill. But spend your entire career as a chef making one signature food, and you're going to get all kinds of bonuses on that food above and beyond your skill rating. See competitive chefs in various categories like chili cook-offs or BBQ cook-offs.)
That's by no means an exhaustive list, but it should give you something to start with.