Combine oats, flour, brown sugar, and cinnamon, then cut in the cold butter until crumbly. Refrigerate the crumble for best texture, and look for even, sandy clumps.

Beat butter and brown sugar until smooth and lighter in color. Add eggs one at a time, then mix in applesauce, sour cream, and vanilla until glossy and fully combined.

Add the dry ingredients to the wet ingredients and mix just until the flour disappears. Fold in the finely diced apple so you see evenly distributed pieces throughout the batter.

Fill the lined cupcake cups about 2/3 full and top each with a generous layer of oat crumble. Bake at 375F for 20-22 minutes, until a toothpick comes out clean and the crumble looks golden at the edges.

Cool cupcakes completely before frosting so the cream cheese sets cleanly. Pipe cinnamon cream cheese frosting around the edge of each cupcake for a thick, sealed border.

Drizzle caramel over the frosted cupcakes in thin lines. Pause to let the caramel slightly set, giving a glossy streaked finish.