Snapedom

I would say that Snape couldn't cook exactly *because* he was a neglected child. One learns to cook by, first of all, experiencing that food is shared, being prepared by someone (usually a caring parent) who would then serve it to you. Neglected children eat on the street, think fish and chips is a gourmet meal and would survive on biscuits, tea and chocolate bars when they're adults.
Theodore Dalrymple in his essay bundle 'Life at the Bottom' tells how he, as a prison doctor, saw numerous undernourished, unhealthily pale inmates come into prison who, after their sentence, left again having gained a fair amount of weight, health and a new experience: sitting at a table, sharing a meal. When he asked these inmates about their past, they were all chucked out of their home by mum (or mum's new boyfriend) when they were 12 or so, and had since that time lived on crisps and bars of chocolate.

Severus was neglected as a child. I doubt his mother or father cooked much, and even if they did, I doubt that young Sev would've spent much time at home if he could avoid it.
Then he goes to Hogwarts, where he eats at a table (will wonders ever cease!) but where the Elves magic the food on the table. No connection with actually *cooking* food.
Then, as an adult, he gets severely and clinically depressed and looses all interest in food (and eating, sleeping and surviving)

So, in short, I doubt Snape can or wants to cook.