• Transfer dough to greased bowl, cover with plastic and store in a warm place until it's doubled in size, about an hour. I like to let the dough rise in the unheated oven.
Finish the filling
• Combine cooled beef with cheese, onions and serranos (if using). Cover and refrigerate until you're ready to use.
Prepare for baking
• Adjust oven racks to upper-middle and lower-middle positions. Line two baking sheets with parchment paper. Cut the paper so it doesn't hang over the sides or else it will get in the way.
• Transfer dough to a lightly floured surface and pull out 10 or 12 equal portions. Place the portions on the baking sheets, and cover with plastic. Let stand 5 minutes.
• Remove one ball at a time from the covered sheets and, using a rolling pin, roll out into 5 ½- to 6-inch rounds. Top with ¼ cup of filling if you're making 12 or 1/3 cup if you're making 10. Pinch the edges of the dough together around the filling. Initially, it'll look like a large empanada. Flip pastry and fold dough underneath. Use your hand to form into ovals and place folded side down back under the plastic. Repeat until dough is exhausted. Make sure runzas are at least 2 inches apart and let rise another 45 minutes.
• Preheat oven to 375 degrees.
• Remove plastic wrap from baking sheets, and brush pastries with egg wash. Bake runzas for 11 minutes. After 11 minutes, swap baking sheets and bake another 11 minutes.
• When runzas are golden brown, remove from oven and allow to cool on wire racks for 15 minutes.
• Serve with fresh guacamole.
Sources: Filling by Dave Cathey, food editor;
Pastry adapted from Cook's Country (July 2012)