On a few occasions, Avery's mother gave her a cookie to keep her quiet when she took her to the grocery store. Now every time Avery goes to the grocery store, she asks her mother for a cookie. This is an example of:

Classical Conditioning (aka Pavlovian conditioning)

Explanation:

Classical conditioning refers to a process of learning by association where two stimuli are paired to produce a specific response. The two stimuli are:

a) a naturally occurring, automatic stimulus called the unconditioned stimulus

b) a neutral event that becomes the conditioned stimulus

The natural response becomes the new learned response and is called the conditioned response.

It was first described by the Russian psychologist Ivan Pavlov at the end of the XIXth century and beginning of the XXth. He observed that during a repeated procedure of feeding dogs, these started salivating since the moment the feeder opened the door, before being presented with their food. This was explained by the association the dogs had established between opening the door and being fed afterwards.

In Pavlov's observation, the unconditioned stimulus was being presented with food, the neutral event was the opening of the door and the response was salivation. After repeating the neutral event along with the unconditioned stimulus, the former became a conditioned stimulus which led to the conditioned response. So, even if the feeder wasn't carrying food to feed the dogs, these had already learned the conditioned response caused by opening the door.

In the question, receiving a cookie was a neutral event associated with a trip to the grocery store. After repeating this a few times, the association was established and that's why now every times that Avery goes to the grocery store she asks for a cookie. This behavior is a learned response.