In a mixing bowl, cream together the sugar and margarine.
Beat in the eggs, then add the flour. Beat together until smooth and even.
Add in the mixed spice and ground ginger and mix. Finely chop the stem ginger, add to the mixing bowl and mix well.
Grease your loaf tin and line with baking paper. Pour in your mixture and cook for approximately 30 minutes, or until cooked. To check if it’s cooked, stick a knife or skewer into the cake, if no residue comes out on the knife, your cake is cooked.
Take out the oven and place on a cooling rack until fully cool.
Place the butter or margarine and icing sugar into a mixing bowl. Mix together until even and soft. Add 2 tbsp of milk and mix until creamy and smooth.
Spread evenly over the top of the cake.
With a pestle and mortar, lightly crush the walnuts and sprinkle them over the buttercream icing. Sprinkle the rose petals over the top to finish the look.