In a 12-inch cast-iron skillet, bring potatoes, 1 tablespoon salt, and water to cover to a boil over medium-high heat. Reduce heat, and simmer until tender, 15 to 20 minutes. Drain potatoes; transfer to an ice water bath. Drain well; thoroughly pat dry. Wipe skillet dry.
In same skillet, cook bacon over medium heat, stirring occasionally, until browned and crisp, about 8 minutes. Remove bacon using a slotted spoon, and let drain on paper towels, reserving drippings in skillet. Melt butter with drippings in skillet.
Using the back of a spoon, gently smash potatoes.
Working in batches if needed, arrange potatoes, garlic, and rosemary in an even layer in skillet. Cook potatoes until browned and crisp, 3 to 5 minutes per side, basting with butter mixture in skillet. Remove potatoes, and let drain on a wire rack or paper towels. Reserve 2 tablespoons butter mixture in a small bowl; wipe skillet clean.
Return potatoes to skillet; sprinkle with pepper and remaining ½ teaspoon salt. Top with bacon and rosemary; drizzle with reserved butter mixture. Keep warm over low heat until serving.
Notes
Whole potatoes can be cooked in step 1 a day ahead and refrigerated. Let them come to room temperature and pat them dry before proceeding with the recipe.
Recipe by Southern Cast Iron at https://southerncastiron.com/garlic-rosemary-crispy-smashed-potatoes/