I really like the idea of potions master Draco who’s really bad at cooking. They’re such similar skills, but have entirely separate needs and requirements.
Potions are easy for Draco–he’s really good at the pedantry of knowing that a potion needs to be stirred precisely 12 times clockwise just before it simmers, or to add exactly 3 beetle eyes before nine dried doxy wings.
Cooking he will never understand, because it’s imprecise. He gets flustered because the instructions aren’t always clear–what direction is he meant to stir in? For how long?–or he focuses too much on what the recipe asks for in absolute accuracy.
If a recipe calls for 55g of butter, he measures to the microgram. He gets agitated when they ask for a “pinch of salt”, because how do you measure a pinch? If a recipe specifies potatoes should be cut into 1cm cubes, he makes sure each cube is 1cm and not a bit more.
He has difficulty knowing exactly when to add ingredients because cooking is an intuitive skill, and doesn’t rely on instructions like, “stir with a copper spoon for maximum potency”.
Some of what he makes is edible. He’s not a total loss in the kitchen, but he watches jealously as Harry bustles around their kitchen, carelessly stirring a pot as he grabs things from the pantry. He huffs when Harry barely glances at the recipe, and then completely ignore it by using ingredients it doesn’t call for, or different quantities.
What really gets him, though, is that Harry has uncanny culinary skills. Whatever he makes is delicious, and Draco can’t figure out why.
He moans about it at Harry every now and then, who always smiles secretively (when he bothers to pay attention to Draco haranguing him). The only thing Harry will say about it, though, is that he’ll keep the secret to himself so Draco will have a reason to keep him around.