Add water, sourdough starter, maple syrup, and flour to a large bowl. Mix with a Danish dough whisk until a shaggy dough forms. Add salt now or during the first stretch and fold. Let rest for 15–30 minutes, then perform a set of stretch and folds or a coil fold to mix well.
Bulk Fermentation
Cover bowl with a loose fitting lid like a plate and leave it in the bowl at room temperature for 3-8 hours to let the dough rise in a bulk ferment. It doesn’t matter if it over ferments, in fact that’s really what you want for focaccia.
Make The Filling
Mix brown sugar and cinnamon. Melt butter and grease a 12-inch cast iron skillet or 9 × 13-inch pan, reserving half the butter.Transfer dough to the pan. Spread half the cinnamon sugar over the dough, fold both sides toward the center to enclose the filling, then flip and gently spread the dough back out.Let rise in a warm spot for 1–2 hours or refrigerate overnight. Chop apples into small pieces. Drizzle the reserved melted butter over the dough and top with remaining cinnamon sugar and apples. Dimple the dough with wet fingers.Preheat oven to 425°F.
Bake
Bake at 425 degrees for 25-30 minutes or until golden brown.
Glaze
Combine powdered sugar and milk in a small bowl to make a thick glaze and drizzle over the top of the warm focaccia.
Slice and Enjoy
Let the focaccia cool before slicing, if you can wait! Store leftovers in an airtight container in the refrigerator for up to one week.If you make this recipe, please leave a 5-star rating to help others find it, too. Happy baking, friends!
Notes
Chop apples into small pieces so they soften while baking. Home-canned apples work great, too.
Use wet fingers to dimple the dough without sticking.
Let the dough rise in a warm spot for 1–2 hours or refrigerate overnight for the second rise.
Grease the pan generously with butter to prevent sticking.
Let the focaccia cool before slicing for cleaner cuts.
Store leftovers in an airtight container in the refrigerator for up to one week.