In a large bowl, combine 4 cups flour, 3/4 cup sugar, 3/4 teaspoon cinnamon, and 1/2 teaspoon nutmeg. Add 1/4 teaspoon kosher salt if using unsalted butter.
In a separate bowl, whisk 1 cup whole milk, 1/2 of the softened butter (4 tablespoons), and 1/2 of the sugar (3/8 cup). Gradually add wet ingredients to dry flour mixture and mix until dough forms.
Roll dough into a rectangle (12×16 inches). Spread 1/2 of the softened butter (4 tablespoons) evenly over dough, then sprinkle 1/2 of the thawed peaches and 1/2 teaspoon cinnamon.
Roll dough tightly into a log and slice into 18 equal rolls.
Place rolls in a lined baking dish, top with remaining peaches and 3 tablespoons butter. Bake at 375°F (190°C) for 35 minutes.
While baking, whisk 1 tablespoon lemon juice with 1/4 teaspoon remaining cinnamon for a syrupy glaze. Retrieve pan, brush glaze on top, and sprinkle streusel made from 1/2 cup flour and 3 tablespoons butter mixed with 1/4 teaspoon cinnamon. Return to oven for 5-7 minutes until golden.
Let cool slightly before serving.