1Brown 1/2 cup (115g) salted butter in a pan over medium-high heat, stirring every 30 seconds until it goes quiet, foams up, and has lightly browned specks.
2Pour the browned butter into a plate or bowl.
3Add 1/2 cup (100g) light brown sugar, 1.5 tablespoons ground cinnamon, and 1/4 teaspoon vanilla extract to the browned butter and mix well to combine, then set aside.
4Peel 2-3 apples.
5Core the peeled apples.
6Dice the cored apples finely.
7Mix 1/3 of the diced apples with half of the cinnamon butter filling.
8Line a 9x13 inch baking tray with parchment paper and brush 2 tablespoons of melted salted butter over the parchment.
9Transfer the focaccia dough to the prepared tray and gently stretch it to the edges.
10Spread the apple and cinnamon filling mixture over the dough.
11Fold the dough over the filling as shown in the video.
12Flip the dough over.
13Cover the dough and let it finish proofing at room temperature for 1-1.5 hours.
14Preheat the oven to 215C/420F, placing the rack in the lowest position.
15Warm up the remaining cinnamon sugar butter filling to a drizzling consistency and mix it with the remaining 2/3 diced apples.
16Spread the apple and cinnamon mixture evenly over the top of the proofed dough and dimple it in.
17Bake for 23-25 minutes.
18While the focaccia bakes, whisk together 125g (1 cup) powdered sugar, 2-3 tablespoons milk, a dash of vanilla extract, and a sprinkle of cinnamon to make the glaze.
19Once the focaccia is out of the oven, drizzle the glaze over it.
20Brush the glaze over the top, sides, and bottom of the focaccia.
21Transfer the focaccia to a cooling rack and let the glaze harden for about 15 minutes.