okay so txf headcannon: mulder knows exactly how scully takes her tea, her coffee, he knows all of her drink orders, he is the Drinks Man (I’ll even venture to say that he can make a mean cocktail) but scully is the one who cooks. mulder is completely inept in the kitchen, like it’s Bad, he knows how to make precisely two things: grilled cheese and spaghetti (and the spaghetti was a Process for him)
firstly, you are very correct about the drinks i can imagine him absolutely committing every single drink scully has ever had to memory. they go out and she gets something new? that is now tucked away in the "things scully likes" folder in his brain and how likely he is to get it for her on a whim while they're out depends on how quickly she drinks it and if she verbally or physically reacts positively to it.
Secondly, he most definitely onows how to make cocktails but I also believe he is absolutely awful at it about 50% of the time. He can pull together some amazing shit. Impressive stuff. But sometimes? He measures so wrong he takes a sip and quite literally can not stop himself from hissing like a vampire drinking holy water. And he often does not secure lids correctly. Both him and scully have been doused in concoctions of juice, soda and alcohol more than once.
Thirdly, I adore the idea of early seasons Mulder now knowing how to cook that's so funny and so sad at the same time. Sad because it shows no one ever took the time to teach him and also shows he really hasn't got time to be looking after himself. Funny because he most definitely has had kitchen disasters. The spaghetti? Be burned it. No fire even needed. One minute it's bubbling away, the next there's hardly any water and the bottom of the pan is black. He assures Scully it had to be aliens messing with his food because there's no way he's that bad at cooking, right? Her giggles make him less upset about the pan he now has to throw away because the damage is... intense.