Step 1
Stir bread flour whole wheat flour and salt together in a large bowl until well combined; set aside.
Step 2
Gently whisk 1 1/4 cups warm water and yeast together in a small bowl. Allow to rest at room temperature until foamy and fragrant about 10 minutes.
Step 3
Make a shallow well in the center of the flour mixture and pour in the yeast mixture. Stir together using a spatula until a coarse dough begins to form. Transfer dough to a lightly floured work surface and begin kneading dusting with more flour as needed to prevent dough from sticking until smooth and elastic about 10 minutes.
Step 4
Shape dough into a ball and place in a large bowl lightly greased with cooking spray. Cover the bowl with a towel lightly dampened with warm water and set aside in a warm spot to rise until doubled in size about 2 hours.
Step 5
Lightly grease a 7- to 8-inch round cake pan with cooking spray and line the bottom with parchment paper; lightly grease parchment paper with cooking spray; set aside.
Step 6
Using your fingers gently press down on dough to deflate slightly and transfer to a work surface that has been very lightly dusted with flour. Gently knead dough 2 or 3 times preserving as many air bubbles as possible. Using the sides of your hands shape dough into a ball by pulling the sides under until a smooth and slightly shiny surface develops. Gently transfer dough to the prepared cake pan and lightly dust with flour; cover tightly with aluminum foil.
Step 7
Add remaining 1 cup water and a steam rack to a multi-functional pressure cooker (such as an Instant Pot®); place cake pan on the rack. Close and lock the lid. Turn vent to Sealing position. Select Manual/Yogurt setting; set timer for 1 hour. Dough will rise in cooker and double in size. Press Cancel.
Step 8
Meanwhile preheat the oven to 450 degrees F (230 degrees C).
Step 9
Select Manual/Pressure Cook setting on the Instant Pot®. Select high pressure according to manufacturer's instructions; set timer for 40 minutes. Allow 3 to 5 minutes for pressure to build.
Step 9
Release pressure using the natural-release method according to manufacturer's instructions 8 to 10 minutes. Unlock and remove lid. Carefully remove the cake pan as it will be hot; remove aluminum foil.