For the cakes: 1 Preheat the oven to 180°C (160° fan) | 350F | gas 4. Grease and line the base of a 23 cm | 9" springform tin with greaseproof paper.
Cream together the butter and sugar in a large mixing bowl until pale and thick, 2-3 minutes.
Combine the ground almonds, polenta, baking powder, and salt in a separate bowl and then beat into the butter and sugar, in thirds, beating in an egg after each addition.
Beat in the orange juice and zest and then scrape the batter into the prepared tin, smoothing the top.
Bake for 40-50 minutes until risen and golden, and a cake tester comes out clean from its centre. Remove to a wire rack to cool.
For the almond cream: Beat the butter in a large mixing bowl until smooth, 2 minutes. Add the sour cream and half of the icing sugar, and stir well. Continue to beat as you add the remaining icing sugar, and then the milk and almond extract.
Spoon about one-quarter of the cream into a piping bag fitted with a star-shaped nozzle. Chill until needed.
To decorate: Pulse the almonds in a food processor until finely chopped. Turn out the cake from its tin. Split in half horizontally, and then cut one half in half again to leave you with three pieces.
Arrange the thick cake on a cake stand. Spread with one-third of the almond cream, spreading out evenly with an offset spatula. Sprinkle over some chopped glacé cherries and then top with one of the remaining pieces of cake.
Top with half the remaining cream, spreading it out evenly and sprinkling with the remaining chopped cherries. Sit the third cake on top, pressing down gently.
Spoon the remaining almond cream on top of the cake and spread it evenly over the top and sides. Gently press the chopped almonds into the sides and edge or the top of the cake.
Remove the piping bag of almond cream from the fridge and leave to stand at room temperature for 5-10 minutes before piping blobs of almond cream around the perimeter of the cake.
Top each blob with a pistachio and arrange the orange slices propped up against the blobs of cream. Cut into slices and serve.