Add 2 Tbsp butter to the Instant Pot and set to the “Saute” setting (for Pressure Cooker, select any of the preset buttons with the lid off). Once melted, add the onions and cook until tender and transparent, stirring occasionally – approximately 5 minutes. Add the chicken broth, salt and pepper, then stir.
Insert your steamer basket or tray into the pot and add the sliced potatoes. Lock the lid in place, select High Pressure for the Instant Pot (for Pressure Cooker, select Beans/Lentils setting) and set time for 5 minutes.
Meanwhile, set your oven to broil, then grease a 9×13 oven safe dish (I used cooking spray). In a small bowl, mix the panko bread crumbs with the 3 Tbsp melted butter and set aside.
When your timer beeps on the IP or PPXL, turn it off and do a quick pressure release. Carefully remove the steamer basket (or if you have a steamer tray, remove the entire inner pot and then carefully remove the tray from the pot without dumping out the liquid in the bottom of the pot) then dump the potatoes into your prepared 9×13 dish.
Stir the sour cream and shredded cheese into the remaining liquid and onions in the pot, then pour over the potatoes. Gently mix the sauce with the potatoes, being careful not to stir too hard or you will have mashed potatoes! Using two forks to stir works great. Sprinkle the panko topping mix over the potatoes and broil for approx 5 minutes or until golden brown. NOTE: be sure to keep a close eye on them as every oven is different and you don’t want them to burn! Allow to sit for a few minutes before serving.