Prepare a batch of same-day focaccia dough following the base recipe up until transferring to the tray
Brown the butter over medium-high heat, stirring every 30 seconds until it turns golden brown with foaming and browned specks
Mix browned butter with brown sugar, cinnamon, and vanilla extract
Line parchment on 9x13 inch tray with 2 tablespoons melted salted butter
Transfer proofed dough to tray and gently stretch to edges
Mix ⅓ of diced apples with half of the cinnamon filling and spread over dough, then fold up
Flip 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 and mix with remaining ⅔ diced apples
Spread apple mixture over dough and dimple in
Bake for 23-25 minutes
Whisk together powdered sugar, milk, vanilla extract, and cinnamon for glaze
Drizzle glaze over focaccia and brush on top, sides, and bottom
Transfer to cooling rack for 15 minutes for glaze to harden
