A word that means to add a small amount of into food (example in body)

Solution 1:

Enhance, Enhanced

This means ‘improved’ and can mean ‘added to’.

If you don’t like the result, (ie, it was not ultimately ‘an enhancement’), you can use the form: ‘When the recipe was enhanced with additional sugar, it unfortunately turned out too sweet’. Or ‘when we tried added sugar as a possible enhancement, it became too sweet, or overly sweet’.

Your examples:

• The food at the restaurant tasted so good that it seemed like the chef enhanced it with crack.

• Even enhancing the cake from this recipe with a small additional amount of sugar made it taste too sweet to be palatable.

Or, Enhancing the cake from this recipe with even a small additional amount of sugar, made it taste too sweet to be palatable.

• The cookies were enhanced with a small amount of chocolate and this made them absolutely irresistible.

Advantages - a fairly neutral word, does not denote a negative addition like ‘laced’.

Solution 2:

In your first and third examples, seasoned would work well - "seasoned with crack" would certainly imply that's something's addictive (or chocolate, a habit with which I'm more familiar).

Your second example is actually a little different. Rather than adding a crucial tiny bit of something special as in your other cases, the cake is spoilt by adding an excess of a major ingredient. If it was ruined by the addition of a little black pepper, seasoned would still work.

In the first case, spiked would also work.