Buckwheat Pappardelle Pasta
Using a flour sifter or fine mesh strainer, sift All-purpose and Buckwheat flours together on a large work surface, making a well in the center of the flours. Place egg yolks and a pinch of salt into a bowl and with a fork break up egg yolks and pour into flour well. Gradually mix ingredients together until just combined; then knead the dough by hand.
Place dough on a lightly floured surface and dust dough with flour. Starting in the middle, push dough away from you with a rolling pin, easing up on the pressure as you approach the edge. Continue rolling dough into a sheet, turning occasionally, until you can see your fingers through the dough. Let dry for 10 minutes.
Dust the top of the sheet of dough with flour and loosely roll into a cylinder. Using a sharp knife, cut into 3/4-inch-wide slices. Unwrap noodles; dust with semolina and gently toss to separate. Place on a sheet pan and cover with a towel until ready to cook (or freeze in freezer bags for up to 2 months).
Cook to al dente (3-5 minutes depending on thickness) in boiling salted water. Drain pasta and set aside.
Making Carbonara Sauce