Potatoes - Firmed when cooked... What to use them for?

Well I brought a BIG bag of potatoes (first time in a while) and used them to cook a potato bake... they tricked me... I cooked them for the time required (45 minutes, then about 10 more to brown)... didn't feel cooked so baked for another 20 minutes, still firm... so decided that we'd "reheat" them tomorrow night instead as dinner was well and truly ready to.

So re-heated them tonight for another 30 minutes, still firm, 5 minutes in the microwave then decided it must be the potatoes, dished them out and yes they taste cook but they weren't soft like the last lot we brought and they weren't as nice :-(

So is this just a type of potato, if so what do I use them for so that they are yummy.... please help

Try mashing them with milk & butter, then dish up or mash them & mix in milk, butter & 1 egg and place on a greased tray in humps and brown in the oven