Peel the potatoes and cut into large chunks.
Place in a slow cooker and pour the broth over the potatoes.
Cook on high for 4 hours, stirring occasionally.
Drain the potatoes over a large bowl and save the broth.
Put the potatoes back into the slow cooker and add the butter and the 1/4 cup reserved vegetable broth.
For a smoother consistency, mix with an electric hand mixer until smooth then add the milk, salt and pepper and mix again. For a chunkier texture, use a hand masher to mash until desired consistency, then add milk, salt, pepper. If dry, add 1-2 Tbsp more milk or broth.
When ready to serve - stir and if it seems like it has thickened add some more of the reserved broth and mix well.