Heat oven to 350°F. Line large cookie sheet with foil or cooking parchment paper.
In 2-quart saucepan, place potatoes and enough water to cover. Add 1/2 teaspoon salt. Heat to boiling; cook 6 to 10 minutes or until tender. Drain.
Meanwhile, in 10-inch skillet, heat oil over medium heat. Cook onion in oil 5 to 7 minutes, stirring occasionally, until softened. Add spinach and broth. Cook 2 minutes, stirring frequently, until broth is absorbed.
In medium bowl, mash potatoes, onion mixture and half-and-half with potato masher or spoon. Add nutmeg, salt and pepper.
Unroll dough on lightly floured work surface. Using 3 1/2-inch round cookie cutter, cut 6 rounds from each dough sheet. (Reroll scraps and cut additional rounds, if desired.) Lightly brush rounds with egg.
Spoon 1 heaping tablespoon potato mixture on half of each round. Fold other half over filling; press edges with fingers or fork to seal. Lightly brush tops with egg. Place on cookie sheet.
Bake 10 to 15 minutes or until golden brown. Serve warm.