In the Instant Pot, add the potatoes with enough water to just cover them.
Add a tablespoon of salt and pressure cook the potatoes in 'Manual' mode, on 'High' setting, for '0' minutes. Let the pressure release naturally.
Once done, take out the potatoes and add them to an ice bath or cold water to stop them from cooking.
Then make thin cuts on the potatoes, letting the knife go around 3-quarters into the potatoes.
Tip: You could insert a skewer or a toothpick lengthwise into the potato, marking the depth to which the knife should make the cut. This helps in making even cuts.
Insert as many garlic slivers as you can into the grooves of the potatoes (see notes if you want to skip this step).
Using a pastry brush, dab on the melted butter on the potatoes. Let the butter get into the grooves.
Tuck in the rosemary sprigs, sprinkle the sea salt and bake in a preheated oven at 180 C or 350 F for 40 minutes.
Serve as a side with the chicken.