In the bowl of a stand mixer fitted with the paddle attachment, add in the following order the water, sourdough starter, bread flour, milk powder, malt powder, butter, and salt.
Start the mixer on low just to combine ~ for 2-3 minutes. Slowly turn the mixer up to medium and mix until well combined and the dough is slightly sticky, about 8 minutes. It’ll be tacky to the touch and barely stick to your finger when touched. If it seems dry, knead in an additional tablespoon or two of water. Lightly spray a larger bowl with cooking spray and place the dough in it. Cover the bowl with plastic wrap and let it rest for 45 minutes. It will rise minimally.
Towards the end of the rising time, preheat the oven to 350°F with the rack in the middle.
Line a baking tray with parchment paper. Depending on the size of your tray/rolls, you may need two. Lightly spray your work surface with cooking spray, NOT FLOUR.
Empty the dough on it and gently fold it over in half, patting it to deflate. Turn the dough 90 degrees, fold it in half, and then fold again. Divide the dough into 8 evenly sized pieces. Pat each piece into a 7-8” long rectangle by 4-5” wide. Evenly divide the cheese amongst the 8 rectangles spreading to 1/2” from the ends with the widest side closest to you.
Evenly diving up the pepperoni, place that along the top of the cheese, spreading to 1/2” from the ends. Starting at the side closest to you (long side) roll up the dough like a jelly roll ensuring the cheese and pepperoni stay put while you roll. When you reach the end, gently pinch the edges together, sealing them all in. Starting at one end, roll the dough into itself (like a snake coiled up). Place the coil on the pan. Repeat for the remaining rolls. *Note: When placing the rolls on the pan, you need to leave about 2” space between each one as they will rise and spread. You don’t want them to touch when they bake.
In a small bowl, whisk together the egg and tablespoon of water until frothy. With a pastry brush, brush the egg mixture on the pretzel. Sprinkle with pretzel salt. Bake for 25 to 30 minutes or until they’re a light golden brown. Remove from the oven and place on a cooling rack.
It is best when eaten on the same day. If not, allow it to cool completely and place it in a paper bag in the fridge.