What I’d like most for dinner is pizza.
What you should do is book your trips in advance.
What was surprising was that you didn’t even tell me what was wrong.
Do/did/does can be added to verb clauses for emphasis in spoken and written English. the main verb is used in the infinitive form without to.
A. None of my friends believe that Mateo and I are cousins because we look so different.
B. Well, that’s nonsense. You do look like brothers!
People always comment that Richard is much fitter than me, but Richard does go to the gym every day, so maybe it isn’t so surprising!
If the main verb is do, do is repeated in the base form after the auxiliary verb.
I do most of the housework, but I do hire a maid sometimes.