Remove crust from bread and cut into 1” cubes to measure 6 cups. Butter a 2 quart casserole or baking dish.
Chop walnuts and toast in oven to a 350º until golden brown, about 5 min, set aside to cool.
In a large bowl, toss together bread cubes, half of walnuts, and butterscotch chips, Pour into prepared casserole dish. Ina saucepan heat 1 cup milk until it just comes to a boil. Add instant coffee, stirring until dissolved, stir in remaining milk.
In a medium bowl, whisk eggs, sugar, and salt, add to milk mixture and whisk to combine well. Pour milk mixture over bread mixture.
Place in refrigerator for at least 1 hour. Preheat oven to 350º.
Sprinkle remaining walnuts evenly over pudding. Cut butter into bits and dot pudding with it. Bake pudding until bubbling and golden, about 40 min.