Place onion, garlic and lemon zest in a food processor. Add 1 tablespoon fresh rosemary (or 1 teaspoon dried) and pulse just until the mixture is finely and evenly chopped (but not mushy).
Transfer the mixture to a medium bowl and gently mix in turkey, breadcrumbs, Parmesan, 1/2 teaspoon salt and pepper until combined. Use a generous 2 tablespoons each to shape the mixture into 12 meatballs (about 1 1/2 inches in diameter). Place flour in a shallow dish and roll the meatballs in it to lightly coat. (Reserve the remaining flour.).
Heat oil in a large nonstick skillet over medium-high heat. Reduce heat to medium, add meatballs and cook, turning once, until brown, 3 to 5 minutes total. Transfer to a plate.
Add wine (or 1/2 cup broth) to the pan, increase heat to medium-high and cook, scraping up any browned bits, until almost evaporated, 1 to 3 minutes. Add the can of broth and bring to a boil. Reduce heat to maintain a simmer and return the meatballs to the pan along with the remaining 1 tablespoon fresh rosemary (or 1/4 teaspoon dried). Cover and cook until the meatballs are cooked through, 8 to 10 minutes. Remove the meatballs to a serving bowl.
Bring the sauce to a boil over medium-high heat and cook until reduced to 1 cup, 4 to 8 minutes. Whisk lemon juice and 1 tablespoon of the reserved flour in a small bowl (discard any remaining flour); whisking constantly, add the flour mixture to the sauce along with butter and the remaining 1/4 teaspoon salt. Simmer, whisking, until slightly thickened, 1 to 2 minutes. Strain the sauce through a fine-mesh sieve. Serve the sauce over the meatballs.