Sprinkle the yeast into the warm water in a small cup and let stand 10 minutes to soften.
Measure the flour by dipping dry measures into the flour container, filling to overflowing, and sweeping off the excess with a straight edge.
Put the flour into a large bowl and stir in the salt.
Cut the cold butter into ½-inch cubes and add to the flour. Use a pastry blender to cut the butter into the flour until particles are the size of small peas.
In a small bowl, beat the egg with a fork to combine the white with the yolk.
Add the sour cream and beat in.
Stir in the yeast.
Add to the dry ingredients and stir together well to make a firm dough.
Shape the dough into a rectangle, wrap in plastic, and refrigerate overnight.
Combine the Parmesan, paprika, and cayenne, and sprinkle generously onto your work surface.
Unwrap the dough and coat all surfaces with the Parmesan cheese.
Roll the dough to a 16 x 8-inch rectangle, adding the cheese often over and under the dough.
Press the cheese into the dough with the rolling pin to incorporate as much of the cheese into the dough as possible.
Fold the right third of the dough over itself.
Then fold the left side over the dough to make a 3-layered packet.
Rotate the dough ninety degrees and roll again to a 16 x 8-inch rectangle.
Repeat the rolling and folding twice more, adding cheese as necessary.
Roll the dough again to a 16 x 8-inch rectangle using the last of the cheese.
Mark the dough into ½-inch widths, and cut with a sharp knife into 32 strips about ¼-inch-thick.
Twist strips several times and place on ungreased cookie sheets (two large 14 x 17-inch cookie sheets, 16 strips on each sheet) pressing firmly on the ends and on the turns of the twist to encourage the strips to stay put.
Refrigerate for 1 hour.
Adjust an oven rack to the center position and preheat the oven to 375 degrees.
Bake one sheet at a time for 15 to 17 minutes, until twists are nicely browned.
When completely cool, store airtight.