Preheat your oven to 350°F (180°C). Grease an 8-inch square baking pan and line it with parchment paper, creating a pleated divider in the center to separate the two cake batters during baking.

In a large bowl, cream together the softened unsalted butter and caster sugar using an electric mixer until the mixture is light, fluffy, and pale in color, which should take about 3 to 4 minutes. Beat in the eggs one at a time, adding a tablespoon of the self-raising flour with each egg to prevent the batter from curdling.

Gently fold in the remaining self-raising flour using a spatula until the batter is just combined and smooth. Divide the cake batter equally into two separate bowls.

Stir the lemon extract and a few drops of yellow food coloring into one bowl of batter until a bright yellow color is achieved. In the second bowl, stir in the raspberry extract and pink food coloring until evenly tinted pink.

Spoon the lemon batter into one side of the prepared pan and the raspberry batter into the other side, smoothing the tops with a spatula. Bake for 22 to 25 minutes, or until a toothpick inserted into the center of each sponge comes out clean and the cakes are springy to the touch.

Allow the cakes to cool in the tin for 10 minutes, then carefully transfer them to a wire rack to cool completely. Once cooled, trim the crusts off the cakes and slice each sponge lengthwise into two equal, long rectangular strips so you have two yellow and two pink strips of equal size.

Lightly dust a clean work surface with powdered sugar and roll out the marzipan into a rectangle roughly 8x12 inches and about 1/4-inch thick. Brush the long sides of all four cake strips with the warmed, sieved raspberry jam to help them stick together.

Assemble the checkerboard pattern by placing one pink and one yellow strip side-by-side on the marzipan, then topping them with the remaining strips in alternating colors. Brush the top and outer sides of the assembled cake block with more raspberry jam.

Carefully wrap the marzipan tightly around the cake block, pressing gently to seal the seam, and trim any excess marzipan. Trim the rough ends of the cake to reveal the clean, perfect checkerboard pattern, slice into thick pieces, and serve alongside a freshly brewed pot of Earl Grey tea.