Slowly pour in milk while stirring until combined and no lumps remain
Cut up butter and add 2 tablespoons to slow cooker
Cover and cook on high for 2-3 hours or low for 4-6 until squash is very tender
Carefully using a potato masher or large fork break up squash into sauce and then stir until well combined and smooth
Add gnocchi and stir to combine evenly
Cover again and cook on high for 15-30 minutes until liquid is absorbed
Melt remaining 2 tablespoons butter in microwave them mix with breadcrumbs and cheese
Top casserole with this breadcrumb topping and either cover and cook on high for another 15-20 minutes OR pop in an oven preheated to 425 degrees for 3-6 minutes in an oven safe dish until lightly browned
Notes
I cooked this on high in my 4 quart casserole slow cooker for 3 hours then on high for 20 minutes for gnocchi. Finally I transferred to the oven for a few minutes to brown the topping.