Preheat and prep the pan. Heat the oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment, leaving a little overhang for easy lifting. Lightly grease the parchment.

Prep the apples. Core and dice two apples into small, bite-size pieces (about 1/4–1/2 inch). No need to peel unless you prefer a smoother texture.

Mix the dry ingredients. In a large bowl, combine 2 1/2 cups rolled oats, 1 1/2 teaspoons cinnamon, 1 teaspoon baking powder, and 1/2 teaspoon salt. Stir to distribute the spices and leavening evenly.

Whisk the wet ingredients. In another bowl, whisk 1 3/4 cups milk, 2 large eggs, 1/3 cup maple syrup (or packed brown sugar), 3 tablespoons melted coconut oil or butter, and 2 teaspoons vanilla.

Combine and fold. Pour the wet mixture into the dry mixture and stir until the oats are well coated. Fold in the diced apples. If using, add 1/3 cup chopped nuts or raisins.

Rest the batter. Let the mixture sit for 5 minutes so the oats hydrate slightly. This helps the bars set up nicely.

Fill the pan. Spread the mixture evenly in the prepared pan. If you like, sprinkle a little cinnamon sugar on top for a light crust.

Bake. Bake for 30–35 minutes, until the center is set and the edges are lightly golden. A toothpick should come out mostly clean with a few moist crumbs.

Cool and slice. Cool in the pan for at least 15–20 minutes. Use the parchment to lift the slab out, then cut into 9–12 bars.

Serve. Enjoy warm or at room temperature. For extra comfort, serve with a dollop of yogurt or a drizzle of warm maple syrup.