Preheat oven to 180C, fan 160C, gas 4. Grease 2x18cm loose-bottomed sandwich tins and line the bases with nonstick baking paper.
In a bowl with an electric hand-whisk or in a food mixer, whisk 450g of the butter and sugar for 5 minutes until light and fluffy, scraping down the sides now and again.
With the motor running, gradually add the eggs and 6 tablespoons of the milk, whisking well after each addition. If it starts to curdle, add a tablespoon of the flour.
Once the eggs have been added, sift in the flour and gently mix in using a large spoon until just combined.
Divide the mixture between the two tins and bake for about 30 minutes until golden, risen and springy to the touch. Leave to cool in the tin for 10 minutes, then turn out on to wire rack and leave to cool completely.
Meanwhile, make the buttercream. Using an electric hand-whisk and a very large bowl, or a food mixer, whisk the rest of the butter until smooth, then whisk in the icing sugar a quarter at a time. Finally, whisk in the vanilla extract, 1 tablespoon of milk and pink food colouring. Set aside.
To decorate, melt the white chocolate in a bowl over a pan of gently simmering water. Coat each ice cream cone in white chocolate, then sprinkle with the sugar stars and leave to set. Place one sponge on a large cake board. Cut the Swiss roll into three equal parts.
Spread about a fifth of the buttercream over the sponge to about 1cm from the edge. Place the second sponge on top. Cover the top and sides with buttercream. Ice the Swiss roll sections with buttercream as well. Place one on each side of the cake and one on top. Smooth the icing by dipping a palette knife into boiling water and then running it over the icing, wiping off the excess icing with kitchen paper as needed. Place a cone on top of each of the Swiss rolls.
Place the Squashies around the top of cake and towers, leaving a gap for the door. Sprinkle the cake with remaining sugar stars. Roll out the white icing, on a clean work surface dusted with icing sugar, to the thickness of a £1 coin. Cut out a door, about 6x8cm, and 3 windows, about 4x5cm each. Decorate by scoring lines on all of them. Press the door on to the front side of the sponge cake and add a tiny blob of pink icing for a door handle. Press a window on to each tower.