Prepare the Dough: In a large mixing bowl, combine 2 cups all-purpose flour, 1/4 cup granulated sugar, 1/2 teaspoon salt, 2 teaspoons baking powder, and 1/2 teaspoon baking soda. Whisk these dry ingredients together until well combined.
Mix Wet Ingredients: In a separate bowl, combine 3 tablespoons melted unsalted butter, 3/4 cup milk, and 1 large egg. Whisk until smooth.
Combine Ingredients: Pour the wet mixture into the bowl of dry ingredients. Stir until just combined, being careful not to overmix. A slightly sticky dough should begin to form.
Add Apples and Spices: Gently fold in the 2 diced apples, 2 teaspoons cinnamon, and 1/4 cup brown sugar. Ensure even distribution.
Shape the Rolls: On a floured surface, turn out the dough and roll it into a rectangle, approximately 12 x 18 inches. Spread a thin layer of melted butter over the dough.
Sprinkle with Cinnamon: Mix an additional 2 tablespoons of brown sugar with 1 teaspoon of cinnamon and sprinkle it over the buttered dough. Roll the dough tightly from the longer edge, creating a log.
Slice the Rolls: Using a sharp knife, cut the roll into 12 equal pieces. Place the rolls upright in your slow cooker, ensuring they are snug but not overly crowded.
Cook on Low: Cover the slow cooker with the lid and cook on low for 2 to 2.5 hours, or until the rolls have doubled in size and are cooked through. Look for a golden-brown top and a firm structure.
Prepare the Icing: In a small bowl, combine 1 cup confectioners’ sugar with a tablespoon of milk until you achieve a smooth, drizzly consistency.
Serve and Enjoy: Once cooked, carefully remove the cinnamon rolls from the slow cooker. Drizzle with the prepared icing before serving. Enjoy warm with a cup of coffee or tea!