Beat the egg in a 350ml heatproof mug with the milk and oil. Blend the coffee with 1 tsp boiling water and add to the mug with the flour, sugar and all but 2 tsp walnuts, mix well to combine.
Microwave on full power for 2-3 minutes or until a skewer comes out clean. Allow to cool.
Sprinkle with reserved walnuts.
Notes
Cooks tipCoffee essence work just as well as instant coffee. You can also serve with whipped cream and a dust of cocoa powder. Add these when sprinkling with the reserved walnuts.