In a large bowl or the bowl of your stand mixer, combine two cups of bread flour with the instant yeast, sugar, and salt. Make a well in the centre and add in the sourdough starter discard and warm water. Stir the mixture into a shaggy dough then knead until a smooth and springy dough forms, about four to five minutes.
Lightly grease a large bowl with non-stick cooking spray and transfer in the dough. Set a dinner plate over the bowl and place in a warm spot to rise for 1.5 - two hours or until the dough has doubled in size.
When the dough has risen, punch it down, form it into a tight ball, and turn it out onto a lightly floured piece of parchment paper, seam side down. Coat the top of the dough with flour, place the greased bowl upside down over top of the dough, and allow it to rise for another 30 minutes or so while you preheat your oven.
Place a large Dutch or French oven fitted with its lid into the bottom third of your oven and preheat it to 450ºF. When the oven has preheated and the dough has risen slightly, use a sharp knife to cut a slit about 2.5 centimeters deep across the top of the dough. Carefully remove the lid from the hot Dutch or French oven, transfer the dough and parchment paper into the oven, splash a little water on the underside of the lid, and quickly place the lid back onto the pot.
Bake the bread covered for 20 minutes then remove the lid and continue to bake for another 20 to 25 minutes or until the loaf is golden brown and hollow sounding when tapped.
Remove the bread to a cooling rack to cool completely before slicing.