Pre-heat the oven to 180°C/160°C /gas 4 and grease your bundt tin with spray oil.
Beat the sugars together with the orange and lemon zest until fragrant.
Add the butter, a cube at a time so it creams with the sugar. Continue to beat until light and fluffy, scraping down the sides every so often.
Add the eggs, one at a time, followed by the vanilla extract.
Sift the flours in a separate mixing bowl with the almonds, baking powder, bicarbonate of soda, mixed spice, cinnamon, nutmeg and salt.
Add the flour mixture into the rest of the batter, alternately with the buttermilk, one third at a time until just combined.
Mix the marzipan, glace cherries, sultanas, currants and mixed peel together in a separate bowl then mix in the extra oat flour to coat. Stir the add-ins into the cake batter until evenly dispersed.
Pour the cake batter into the bundt tin and bake for about 75 minutes or until an inserted cocktail stick is removed clean. Check the cake at 30 minutes and cover loosely with foil if the cake is browning too much.
Remove from the oven, and leave for 5-10 minutes to rest in the tin before carefully turning out to finish cooling on a wire rack.
Mix the icing sugar with the lemon juice a little at a time until smooth and thick but just pourable.
Stir in the almond extract.
Spoon the icing over the top of the cake.
Weigh out eleven 25g pieces of marzipan.
Roll each marzipan piece between the palms of your hands into the shape of small eggs.
Place the eleven marzipan eggs around the top of the cake.
Oat Flour. If you can't digest oats then use sorghum flour in its place.Buttermilk. If you don’t have any buttermilk then use 350ml whole milk + 1½ tbsp. lemon juice. Whisk together then let sit for five minutes before adding to your cake batter.Marzipan. Homemade Marzipan is so quick and easy to make. It will take your cake from delicious to stunning.Add-ins. Stir 2 tablespoons of oat flour into the add-ins to coat them and help them evenly disperse throughout the cake.Storage. This Simnel Cake will keep for up to a week in an airtight tin in a cool dark place. However if you are using Homemade Marzipan balls then they should be eaten within three days due to the raw egg in the dough.