Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Add butter, leeks, and salt and saute until tender, 3 to 5 minutes.

Reserve 1/4 cup cubed potatoes. Add remaining potatoes to the pot with the leeks. Place reserved potatoes in a steamer basket and add basket to the pot. Pour in chicken broth.

Close and lock the lid. Set timer for 10 minutes. Allow 10 minutes for pressure to build.

Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid.

Remove steamer basket and set steamed potatoes aside. Add half-and-half. Blend soup using a stick blender and stir steamed potatoes and seasoned salt into the soup. Serve immediately.