Prepare a batch of same-day focaccia dough.
While the dough is proofing, make the cinnamon sugar butter filling.
Mix the browned butter with the brown sugar, cinnamon and vanilla. Set aside.
When the dough has finished proofing, line the parchment on the tray with 2 tbsp melted salted butter.
Transfer the dough to the tray (9x13 inch) and gently stretch the dough to edges.
Mix ⅓ of the diced apples with half of the cinnamon filling, spread over the dough and fold up.
Flip the dough over and cover to finish proofing at room temp for 1-1.5 hours.
Preheat oven to 215C/420F, place rack in lowest position.
Warm up the cinnamon sugar butter to make it drizzling consistency again.
Mix with the remaining ⅔ diced apples, spread over the top of dough evenly and dimple in.
Bake for 23-25 minutes.
Whisk up the glaze: powdered sugar, milk, vanilla extract, and cinnamon.
Drizzle over the focaccia once it’s out of oven, brush on top, sides and bottom.
Transfer to cooling rack for glaze to harden (about 15 mins!).
