To make the filling: Blanch the broccoli rabe in salted boiling water for 4 minutes. Drain immediately, rinse thoroughly, and set aside.
In a large skillet, combine the olive oil, red pepper flakes, and garlic and sauté over medium-low heat until softened, about 3 minutes. Add the broccoli rabe and stir. Cover and cook over medium-low heat for a minute or two until tender. Toss frequently to ensure even cooking. Using a slotted spoon, transfer the broccoli rabe to a plate and let cool.
To make the dough by hand: In a small bowl, combine the yeast and ¼ cup of the warm water. Let stand in a warm place for about 10 minutes, or until foamy. Sift 1 cup of the flour and the salt together into a large bowl. Make a well in the center. Add the remaining ¼ cup warm water and the 2 tablespoons olive oil to the yeast mixture and pour the liquid into the well.
Using a wooden spoon, gradually stir the flour into the liquid until the dough becomes too stiff to stir with the spoon. Using your hands, form the dough into a ball. On a lightly floured board, knead the dough for 8 to 10 minutes, or until silky and elastic, adding flour as necessary to keep it from sticking.
To make the dough in a food processor: In a small bowl, combine the yeast and ¼ cup of the warm water. Let stand in a warm place about 10 minutes, or until foamy. Combine the flour and salt in the processor and pulse to blend, about 30 seconds. Add the remaining ¼ cup warm water and the olive oil to the yeast mixture. Stir gently and pour into the processor. Process until a ball has formed, about 40 seconds.
Transfer the dough to a lightly floured board and knead until silky and elastic, 3 to 4 minutes.
Put the dough in a lightly oiled large bowl. Lightly brush the surface of the dough with oil. Stretch plastic wrap tightly across the bowl, covering it completely. Let the dough rise at room temperature until doubled, 1 to 2 hours. If the dough rises too quickly, punch it down and let it rise again.
Preheat the oven to 450°F with a baking stone inside. Sprinkle a baker’s peel with cornmeal. If you don’t have a baking stone and peel, sprinkle a baking sheet with cornmeal.
Punch down the dough and transfer it to a lightly floured board. Knead for several minutes, until elastic. Flatten the dough into two disks. Working from the center of each disk outward, press and stretch the dough to make a ¼- to ½-inch-thick round. Turn the dough over several times as you stretch it to prevent it from shrinking back. Transfer the dough to the prepared baker’s peel or baking sheet. Cover with kitchen towels and let rise for 30 minutes.
Brush the dough lightly with olive oil. Drain the broccoli rabe and spread it over half of the dough, leaving a 1-inch border. The filling should not be thicker than about ½ inch. Pull the other half of the dough over the topping. Crimp well to seal. Using a fork, pierce the top of the pizza with plenty of holes. Brush the surface with the beaten egg. If using a baking stone, slide the pizza off the peel or baking sheet directly onto the stone. Otherwise, bake the pizza on the baking sheet. Bake until crust an even golden color, about 30 minutes. Remove from the oven and let stand for 5 minutes before cutting. Serve hot or warm.