For Pretzels

1. Combine the flour, sugar, yeast, and salt in a large bowl. In a separate pan melt the butter and add to the flour mixture and mix well. Add the egg and stir well.
2. Transfer to a large lightly oiled bowl and leave in a warm place for 1 hour until it has doubled in size.
3. Meanwhile, bring the 10 cups of water and baking soda to a boil in a large saucepan.
4. Turn the dough onto a lightly floured work surface and divide it into 6 pieces, and roll each to form a long rope. Cut each rope into 1-inch pieces to form pretzel bites.
5. In batches, add the bites to the boiling baking soda mixture for 30 seconds, and remove with a slotted spoon and onto an oiled baking sheet.
6. Brush the bites with egg wash and sprinkle with a little Koster salt.
7. Bake in a preheated oven for 15 minutes.

For Cheese Sauce

1. Melt the butter in a heavy-bottomed saucepan and stir in the flour. Gradually pour in the milk and whisk until the mixture thickens. Stirring constantly mix in the cheese and season.
2. Transfer into a bowl and serve with pretzel bites