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In Kotlin, the typical method for creating a new map with extra key-value pairs added to an existing immutable map is to use the plus operator.

For example, suppose we have an immutable mapOf a few key-value pairs:

val map1 = mapOf("a" to 1, "b" to 2, "c" to 3)

We can create a new map with an extra key-value pair added to it by using the plus operator:

val map2 = map1.plus("d" to 4)

This creates a new immutable map map2 which includes all the key-value pairs from map1 as well as a new key-value pair "d" to 4. Note that map1 is not modified by this operation as it is immutable.