I think that you made a good attempt for translating the question word by word:
What is your favorite meal to cook?
Que es tu favorita comida a cocinar?
But a better way to translate will be:
Cual es tu comida favorita para cocinar?
The reason of why is better to translate "What" to "Cual" is because the question implies that you have to choose, mentally, your favorite from a variety of meals. In English when you ask to pick or choose you use "Which" ("Cual" stands for "Which" in Spanish, they are exact equivalents).Of course you won't use "Which" in that question because you want to know the name of the meal, but in Spanish, that doesn't sound good, considering what I explained.
"Para cocinar" instead of "a cocinar" is simple. "Para" is used to express the purpose of cooking but "a" doesn't.
We say "comida favorita" because in Spanish you normally write the subjective first and the adjective after.
For the translation of the answer, it should have been:
Mi comida favorita para cocinar es Paella.