The next morning, in the bowl of a stand mixer, mix together the risen leaven, water, flour, salt and malt powder using a dough hook. The dough will be very thick, almost crumbly at first, but will come together as you add the butter.
Within the first minute or two of kneading, add the softened butter, 1/2 Tablespoon at a time and knead for 5-6 minutes until completely incorporated.
Let dough rise for 4-6 hours until puffy and just about doubled in size. After the first hour, perform one stretch and fold: reach down onto the side of the dough, pull the dough up and stretch it over the top, pushing it back down onto the other side of the dough. Rotate the bowl and repeat two or three more times as you go around the bowl. The warmth of your dough/kitchen will determine the length of rise time, though this is typically 4-6 hours.
After 4-6 hours, pre-shape the dough into 12 equal-sized balls, cover and rest for 20 minutes at room temperature.
Shape the pretzels by rolling them into a long rope. Begin rolling in the middle and then easing your way out. The middle of the "rope" should be thicker than the ends. Pull the thinner ends up, twist and press down into the pretzel. Watch this video to see how I shape my pretzels. See recipe note for pretzel rolls.
Place pretzels on a parchment lined baking sheet. Stick in the fridge for 1 hour.