Alcohol added to a recipe may cook off, but it depends on how long you cook it. Rena Cultrufelli of the USDA prepared the following table of alcohol content in cooked foods.
Preparation Method = Percent Retained

Alcohol added to boiling liquid and removed from heat = 85%

Flame = 75%

No heat; stored overnight = 70%

Baked, 25 minutes, alcohol not stirred into mixture = 45%

Baked/simmered, alcohol stirred into mixture:

15 minutes = 40%
30 minutes = 35%
60 minutes/1 hour = 25%
90 minutes/1.5 hours = 20%
120 minutes/2 hours = 10%
150 minutes/2.5 hours = 5%

So you see not all the alcohol is ever complete “burned” off.