Heat oven to 160C/140C fan/. Grease a 900g loaf tin and line with a strip of baking parchment. Cream the butter and sugar for the Christmas trees together until light and fluffy. Beat in the 3 eggs separately, mixing well after each addition. Sift together 140g flour and 1⁄2 tsp baking powder, then fold into the mixture along with the almonds. Combine 100ml milk, 11⁄2 tsp vanilla and a good amount of the green food colouring and add to the batter, then mix until evenly coloured.
Pour into the prepared loaf tin and bake for 1 hr until a skewer comes out clean, covering with foil if it gets too dark in colour. Cool for 10 mins in the tin, then transfer to a wire rack. When cool, cut the cake into slices. Using a cutter, stamp out Christmas trees and save the leftover green cake for eating!
Repeat the process to make a second cake mixture then pour 1⁄2 of the mixture into the prepared loaf tin. Push the bottoms of the trees into the batter in a tightly packed row. Spoon over the remaining cake mixture, covering the trees and bake for 1 hr or until a skewer comes out clean. Cool for 10 mins in the tin, then transfer to a wire rack to cool completely.
To make the icing, combine the butter, sugar and condensed milk in a bowl and mix until thick and fluffy.
Sprinkle with the toasted almonds and add the sugar cranberries. Finish with a few sprigs of mint and serve straight away.