How to make users choose at least one option in a list but allow additional selections

We know that radio button groups are used to limit user input to just one selection in a list of items, and that checkboxes are used to let users select from 0 to a set number of options from a list of items.

What is a commonly accepted design pattern to ensure that the user will select at least one item from the list, but can optionally select additional items. It doesn't seem to fall into the typical use cases for checkboxes, and using a dropdown list that has line items that can be checked or unchecked also doesn't seem to be very intuitive.

Is the best way to make this clear to the user to provide labels and guidance? Are there other UI elements or design strategies that work better?