Scrub the potatoes well, but don't peel. Line a bowl with a cloth. Grate the potatoes into it, then squeeze out the liquid into the bowl and let it sit for about 20 minutes until the starch settles. Set the potatoes aside.
Drain off the water and leave the starch in the bottom of the bowl. Add the grated potato, a handful of flour and some salt.
Melt a nice bit of butter on a heavy iron pan and pour in the potato mixture. It should be 3/4-1 inch thick. Cook on a medium heat. Let it brown nicely on one side before turning over and then on the other side, about 30 minutes in all depending on the heat. It's much better to cook it too slowly rather than too fast. It should be crisp and golden on the outside. Cut the boxty into four wedges and serve.
Recipe courtesy of Irish Traditional Cooking: Over 300 Recipes from Ireland’s Heritage by Darina Allen/Kyle Books, 2012.