Adjust oven rack to upper-middle position, about 5 inches from heating element; heat broiler. Whisk eggs, half-and-half, 1/4 teaspoon salt, and 1/8 teaspoon pepper in medium bowl until well combined, about 30 seconds. Set eggs aside.
2. Fry bacon in 10-inch nonstick ovensafe skillet over medium heat until crisp, about 10 minutes. Using slotted spoon, transfer bacon to paper towel-lined plate; pour off all but 1 tablespoon of bacon fat. Add potatoes to skillet and cook, stirring occasionally, until golden brown and tender, 10 to 15 minutes. Stir cheddar, scallions, and bacon into eggs; add egg mixture to skillet and cook, using spatula to stir and scrape bottom of skillet, until large curds form and spatula begins to leave wake but eggs are still very wet, about 1 minute. Shake skillet to distribute eggs evenly; cook without stirring for 30 seconds to let bottom set.
3. Slide skillet under broiler and broil until frittata has risen and surface is puffed and spotty brown, 1 1/2 to 2 minutes; when cut into with paring knife, eggs should be slightly wet and runny. Remove skillet from oven and let stand 5 minutes to finish cooking; using spatula, loosen frittata from skillet and slide onto platter or cutting board. Cut into wedges and serve.
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