Can you make cornbread if milk is expired but does not smell?

The date on milk is generally a 'sell by' date. You can expect the milk to remain good for 5 to 7 days after that, as long as it has been stored properly and has been kept below 40°F.

Since the milk is being cooked, if it doesn't smell, hasn't curdled and is just a few days past the sell by - you shouldn't have any problem.