Mill 500g hard white wheat berries. You can substitute part of the flour with other grains, but make sure at least half is hard wheat so the dough has enough gluten strength. My favorite combo is 350g hard white wheat & 150 soft white wheat
In a medium mixing bowl combine 430g warm milk, 30g honey, ½ tsp salt, 56g room temp butter, 2 tsp vanilla, 1½ tsp instant yeast, and 500g fresh milled flour. Mix together until a shaggy wet dough forms, cover and let the dough rest 15-20 minutes.
Uncover your bowl, stretch the corner of the dough as far as it will go without ripping, then fold it over itself to the center of the bowl. Turn your bowl and repeat this to each corner. Cover your bowl and let it rest 15 minutes. Repeat stretch and folds every 15 minutes for an hour, totaling 4 sets.
After 4 sets of stretch and folds, cover and let your dough rise at room temperature until doubled, about 1 hour.
Peel and finely dice 3 apples. In a small sauce pot, place 115g (½ cup) butter. Keep over medium heat until the butter is crackling, browned, and gives off a nutty aroma. Remove the butter from the heat and add 100g (½ cup) light brown sugar, diced apples, 2 tbs cinnamon & ½ tsp salt. Mix well and set aside.
Fill a 9×13″ baking dish with parchment paper. Drizzle 2 tbs melted butter over the parchment paper. Gently scrape the dough into the pan and stretch it toward the edges, until it fills the pan. Pour 1/3 of the apple cinnamon mixture over the dough, fold it over itself so the apples are in the center of the dough (this will create nice layers) and gently pull the dough back to the corners. Cover and let rise until puffy and nearly doubled, 1–2 hours.
About 30 minutes before baking, preheat oven to 450°F (245°C), with the rack near the bottom.
When the oven is preheated and the dough is ready to be baked, spread the rest of the apple mixture evenly over the dough. Use your fingertips to press deep dimples every 1–2 inches, letting the glaze pool in the indentations.
Bake at 450°F (245°C) for 20-25 minutes, until golden brown and bubbly.
While the bread bakes, mix together 60g milk, 1 tsp vanilla, and 110g powdered sugar until smooth.
Let the focaccia cool in the pan for 5 minutes, then transfer to a wire rack. Drizzle with glaze. Let it rest for 15 minutes and the glaze will slightly harden. It is best served warm, fresh from the oven!