1. Bake TWO round 15 cm cakes and TWO round 20 cm cakes using the Vanilla Sponge Cake recipe.
2. Make the royal icing
Beat egg white in an electric mixer, using the whisk attachment, on a slow speed until bubbles start to appear.
Add sifted icing sugar a little at a time, beating on a higher speed until it forms firm peaks.
Add lemon juice and mix in gently. Tightly cover the icing with plastic wrap as soon as it is made so it doesn’t dry out.
Note: Royal icing will keep in an airtight container in the fridge for up to 10 days. Remove from the fridge, bring to room temperature and stir well before using.
Colour royal icing pale pink by using the tip of a toothpick to add a tiny amount of red colouring then mixing well. Continue adding a little at a time and mixing well until desired tone is reached.
3. To Make The Turrets: Use a pastry brush to paint the pink royal icing over the outside of the flat-based cones. Press 8 cones together, base to base, to make 4 pairs, leaving 1 cone unattached. Set the cones aside to dry, standing them upright.
Pour the pink sugar sprinkles into a shallow bowl. Spread the royal icing over the pointy cones, roll the cones in pink sugar sprinkles, and set them aside to dry, standing them upright. Once the cones are dry, attach a sugar-covered cone to the top of each turret, as well as to the unattached cone, with a little royal icing. Set the cones aside to dry.
4. Make the buttercream
Beat butter in an electric mixer, using a paddle attachment, until the butter lightens in colour. Slowly add icing sugar in small batches (so it doesn’t fly out of the mixing bowl), beating in between until combined. Add milk 1 tablespoon at a time.
Note: Start with room-temperature butter (not melted) and to beat with an electric mixer until the butter turns from a yellow to a white tone before adding icing sugar. If necessary, make buttercream in two batches, mixing together at colouring stage to ensure consistent colour. Buttercream can be stored in an airtight container for up to 2 weeks in the fridge, but bring it back to room temperature and beat again before using so it is as light, fluffy and soft as possible.
Colour buttercream pink, again by using the tip of a toothpick to add a tiny amount of red colouring then mixing well. Continue adding a little at a time and mixing well until desired tone is reached.
5. Level the cakes using a cake leveler if possible. Turn cakes over.
6. Cover the top of one 20 cm cakes with buttercream and place the other 20 cm cake on top. Place the 20 cm cake stack on a serving plate. Cover the top of one 15 cm cakes with buttercream and place the other 15 cm cake on top.
7. Support and stack the cakes by inserting a skewer all the way down into the 20 cm cake and use a pen or a knife to mark the skewer where it enters the cake. Pull out the skewer and cut where marked. Using your first skewer as a guide, cut four more skewers to the same height and push them into the cake: one in the middle then four surrounding the central skewer halfway between the centre and the outside edge of the cake. The top of the skewers should be flush with the top of the cake.
Stick the bottom of the 15 cm cake stack to the cake board using a small amount of buttercream and place on top of the larger cake stack. The weight of the smaller cake will be supported by the skewers in the larger cake underneath.
Cover the cake with buttercream to a smooth finish. Press the 4 tall cone turrets into the buttercream around the base of the cake. Press mini marshmallows into the buttercream in a brick pattern all the way up the sides of the cakes, using royal icing as glue if necessary.
8. To Make The Battlements: Press a row of mini marshmallows around the top edge of both tiers, leaving even gaps in between.
Stick a dowel or a skewer through the bottom of the shortest cone turret and use the skewer to anchor it to the top of the cake stack.
9. To Make The Door: Cut the top two corners off the pink ice cream wafer to form an arch shape. Stick the door to the front of the cake with royal icing. To make the door handles, stick 2 silver cachous to the middle of the door with royal icing.