Preheat the oven to moderately hot 200 degrees C and lightly grease two baking trays.
Cook the potatoes in boiling salted water until just tender. Drain and put through a food mill or mash smoothly in a bowl. Add the butter and flour and a little salt, to taste. Mix together to form a rough dough, then knead 10-12 times on a lightly floured surface until soft and smooth.
Divide the dough in half. Roll each half out into a rectangle a little larger than 16 x 8 cm. Trim it down to that size with a sharp knife and cut in half. The trimmings can be re-rolled. Now cut the dough into 1 cm sticks across the width and place on the trays leaving room to spread. Brush with poppy seeds and then a little salt. Bake for 10-12 minutes, or until golden.
Recipe Notes
These breadsticks can be kept in an airtight container for up to five days and crisped in the oven.