How to Make It
Whisk together sugar, flour, butter, eggs, cocoa, instant coffee, salt, and vanilla in a large bowl until smooth. Generously coat a 3-quart round or oval slow cooker with cooking spray. Pour batter into slow cooker. Drape a clean kitchen towel over slow cooker, and place lid over towel. Pull towel taut under lid. Cook on LOW until edges are set, about 3 hours. Remove insert from slow cooker to a wire rack, keeping towel and lid in place. Let stand until center is mostly set, about 30 minutes. Scoop warm pudding cake onto individual plates, and dust evenly with powdered sugar. Serve immediately with ice cream if desired.