why does the auther use"make"not "made "here?Thx.
Well I heard that naughty boys and girls get coal in
their stockings, so I thought I’d be nice and make
Santa cookies.I even left out some milk. I heard
someone in the kitchen eating the cookies, so I
came downstairs!
why does the auther use"make"not "made "here?Thx.

Question

Answer

Both the verb 'be' and the verb 'make' are part of the conditional construction following 'would'.  The fuller form is : I thought I'd be nice and (I'd) make Santa cookies.

Answer

Because the author is speaking prospectively - I thought I would be nice and would make some cookies.  If they had been speaking retrospectively, they could have said - I decided to be nice, and made some cookies. I can see why this might be difficult to understand!