Line the insert of a 4 or 6-quart slow cooker with a large piece of non-stick foil or use regular foil and butter well.
Whisk together the melted butter, sugar, cocoa powder, flour, eggs, vanilla, and salt in a medium bowl.
Fold in the chocolate chunks.
Pour the batter into the prepared slow cooker in an even layer.
Cover and cook on low for 3 hours or till cake is set around the edges and gooey in the center.
Serve the cake warm, scooped into a bowl, and topped with ice cream.
