Combine the discard, flour, room-temperature butter, sour cream, salt, and grated cheese in a big bowl. Start mixing with your hands and add water until you get a homogeneous dough.
Form a ball of dough and split into 4 equal balls (weighing is not necessary, but it helps with keeping all the balls the same size).
Start rolling out one of the dough balls into a rectangular of approx. 9"x7.5" (23cmx19cm), using two sheets of parchment paper, one on the bottom and one on top.
Grate the cheese directly on the dough, generously covering the entire surface (measure with the heart). Generously sprinkle with sea salt flakes, sesame seeds, and poppy seeds.
Start tightly rolling the sheet with the help of the parchment paper. When rolled, wrap it in a film and put it in the fridge for 40 minutes (or you can wait until all of them are ready and put them all at the same time).
After 40 minutes have passed, start preheating the oven to 350F/180C. Take the rolls out and slice each roll, with a pastry cutter or a good knife, into slices of about 1/2" (I slice each roll in about 13 pieces).
Arrange them on a baking sheet lined with parchment paper, and bake them for 20 minutes. After 20 minutes, take the baking sheet out, and flip each roll so the face that was down is now up. The face down should be golden brown.
Bake them for about 5-7 more minutes or until the face down is also golden brown. As ovens may vary, keep an eye on them. They should be crusty and hard when done.
Let them cool down on the baking sheet for about 10 minutes, then arrange them on a serving platter.