In a small saucepan, combine the coconut butter, cocoa powder, sea salt, milk, and maple syrup over very low heat (or use a double boiler for better heat control). Whisk through until the coconut butter is melted and all the ingredients are smooth. Transfer to a glass dish to let cool. Refrigerate until completely chilled, then use for spreading between cookies for cookie sandwiches, and as a thick frosting for cakes or brownies.