Melt butter: Place 90 grams (some will evaporate so use a bit more than dough calls for) unsalted butter in a pan or small pot to melt. Once melted, remove from heat and set aside.
Scale: Place a large mixing bowl on the scale. Tare the bowl then add the flour, brown sugar, white sugar, baking powder, and salt (Remember to use the scale’s tare function to remove the weight of the bowl and previous ingredients to only weigh the current item added)
Stir: Stir dry ingredients together. Make a well in the center. Set aside.
Mix wet ingredients: In a second large mixing bowl, scale in sourdough discard, eggs, milk, vanilla extract, and 84 grams of the melted butter (should be warm, no longer hot).
Add wet ingredients: Pour wet ingredient mixture into the center of the dry mixture.
Stir: Stir together, don’t over mix. All ingredients should be well dispersed through dough. It should be a thick batter. You can proceed with the next steps, or for more flavor and fermentation, you can cover the batter and let it sit for 30 to 60 minutes or overnight in the fridge.
Preheat: Preheat oven to 350º
Prepare apple cinnamon mixture: Peel and dice apples. Place in a small bowl. Add sugar and cinnamon. Toss together to combine well.
Prepare loaf pans: Cut a square piece of parchment, at least 12-by-12-inch. Turn a loaf pan over, center the parchment over the bottom of the loaf pan. Use scissors to make four cuts from the edge of the paper to each corner. Turn loaf pan over. Use cut slits to fold edges in to fit parchment snugly into loaf pan.
Fill loaf pans: Use a spatula to add half of the dough to the loaf pan, spread to fill bottom of pan. Top with half of the apple cinnamon mixture, gently press apples into the dough. Add the rest of the dough, spread to cover the apple layer. Top with the rest of the apple cinnamon mixture, gently press apples into dough.
Make streusel: Add softened butter and brown sugar to a small bowl. Stir with a fork until it becomes a streusel mixture that can be crumbled over the dough in the loaf pan. Evenly top the apple fritter bread with the streusel.
Bake: Place pan into oven and bake 60 to 70 minutes. The bread should have a carmelized crust, golden brown edges on the dough, and a toothpick or knife inserted into the center should come out clean.
Cool: Allow to cool for about 20 minutes.
Prepare glaze: While bread is cooling, whisk glaze ingredients together until drizzling consistency. When bread is cool, drizzle generously with the vanilla glaze.
Serve: Cut the bread into slices and serve.