Add all the soup base ingredients, carrots through rosemary, to the Instant Pot and stir to combine. Cover, seal the lid, and cook on manual/high pressure for 40 minutes. When finished, use the quick release function to vent steam. Open the lid and toss in the kale, leaving the Instant Pot on the keep warm setting.
To make the roux, melt butter in a medium saucepan over medium heat. Whisk in the flour, and cook for 1-2 minutes. Gradually add the milk, whisking constantly, until the sauce is thick and smooth.
Pour the roux into the Instant Pot, stir everything together to combine well, and serve. Enjoy!