Preheat the oven to 350 degrees F. Grease a 13 x 9 baking dish with the butter.
Tear the bread by hand into large pieces and place layers into the baking dish, alternating with the berries so that they are evenly distributed.
In a large bowl, combine the milk, cream, sugar, eggs, salt and cinnamon and whisk together. Pour over the bread in the baking dish and evenly distribute. Press with a spatula all over the surface so that the bread soaks up the liquid evenly.
Place in the oven and cook for 75 minutes.
Meanwhile make the sauce by adding the berries and sugar into a large sauce pot over medium heat. Bring to a low simmer, stirring often until the berries break down to a jam consistency. Cook for about 1 1/2 hours and in the last 30 minutes add the brandy.
Serve a scoop of the bread pudding while still warm with the dewberry sauce drizzled on top. Add a scoop of your favorite ice cream as well if you please.