Prepare a batch of same-day focaccia dough following the base recipe instructions up until transferring to the tray
While dough is proofing, make the cinnamon sugar butter filling by mixing browned butter with brown sugar, cinnamon, and vanilla extract
Line parchment on a 9x13 inch tray with 2 tablespoons melted salted butter
Transfer proofed dough to the tray and gently stretch to edges
Mix ⅓ of the diced apples with half of the cinnamon filling and spread over the dough, then fold up
Flip the dough over and cover to finish proofing at room temperature for 1-1.5 hours
Preheat oven to 215°C/420°F with rack in lowest position
Warm the remaining cinnamon sugar butter to drizzling consistency, mix with remaining ⅔ diced apples, spread over dough and dimple in
Bake for 23-25 minutes
While baking, whisk together powdered sugar, milk, vanilla extract, and cinnamon for the glaze
Drizzle glaze over focaccia once out of oven, brush on top, sides and bottom
Transfer to cooling rack for 15 minutes to allow glaze to harden
