If using dough stored in the refrigerator, place on a lightly floured surface, gently press into a 5-inch flat circle and cover with plastic wrap about two to three hours before you plan to bake the pizza. However, if you made your dough right away and it's already risen and come to room temperature, you're ready to skip straight to step 2.
About 45 minutes to an hour before baking, place a pizza stone in the cold oven and turn the heat to 500 degrees. If you don’t have a pizza stone, you can use a large baking sheet and preheat for 30 minutes, though a pizza stone is recommended for best results.
Place bacon in a cold skillet and turn the heat to medium. Heat the bacon until it's cooked half way. Reserve on a paper towel-lined plate.
Wipe out the excess bacon fat. Melt the butter. Whisk in the flour and cook for three to four minutes, whisking continuously. Pour in the chicken stock and whisk until there are no lumps. Continue to cook until the mixture thickens and then stir in the sour cream. Taste the sauce. If desired, add salt and pepper to taste. Set the sour cream sauce aside.
Hand stretch the dough using the bed of your fingers rather than your finger tips to pat the dough outward toward the edge. Don’t pat in the center of the dough, or you’ll get limp pizza. Really focus on staying outside of the center and work toward the edge. After you work the dough, grab the edge of the pizza and lift it in the air. Allow it to quickly hang down and keep rotating the pizza crust through your fingers to allow the rest of the pizza to have a chance to hang like you’re turning the steering wheel of a car. Do not use a rolling pin to shape and flatten. The dough is stretched when it’s 10 inches in diameter. If any holes form, pinch the dough back together.
Coat a pizza peel or the back of a parchment paper-covered baking sheet with cornmeal and place the hand-stretched dough on top. Adjust the shape if necessary.
Spoon the sour cream sauce on the dough, leaving room for the crust. Depending on how saucy you like your pizza, you might not need all the sauce -- it comes down to personal preference. Sprinkle the mozzarella and cheddar on top and then add the par-cooked bacon and potato slices.
Whisk together the egg yolk and water and brush on the crust.
Transfer to the hot pizza stone. If using parchment paper on a baking sheet to transfer the pizza, bring the baking sheet to the edge of the pizza stone, grab the edge of the parchment paper and slide the pizza from the baking sheet to the pizza stone. Bake for two minutes, remove the parchment paper and then continue to bake for six to eight minutes. If using a pizza peel with no parchment paper to transfer the pizza directly to the stone, bake for eight to 10 minutes.
Remove from oven. Let the pizza set for about five minutes, cut into slices and top with chopped green onions. Enjoy!