Cut the butter into cubes and leave at room temperature to soften.

Break up the chocolate into 2 cm pieces.

Lightly beat the eggs.

Preheat the oven to 180ºC.

Grease the square tin and line with parchment paper.

Lift the Chef Patissier XL head and fit the heat shield.

Fit the Creaming beater to the machine.

Attach the EasyWarm bowl to the machine.

Add Ingredients 1 (butter, chocolate) into the EasyWarm bowl, fit the splash guard.

Heat at heat setting 7 on Stir Speed 1 for about 15 minutes until melted.

Remove the bowl from the machine and set aside.

Remove the EasyWarm bowl from the machine.

Attach the Mixer bowl to the machine.

Remove the creaming beater, fit the whisk tool.

Add Ingredients 2 (sugar, eggs, vanilla) to the bowl.

Mix on speed Max for about 2 minutes until light and fluffy.

Remove the whisk tool, fit the K beater.

Transfer the melted chocolate from the EasyWarm bowl into the Mixer bowl.

Add the first two items of Ingredients 3 (flour, salt) into the Mixer bowl.

Mix on speed 1 for 30 seconds until combined.

Add the remaining Ingredients 3 (white chocolate chips) into the bowl.

Mix on speed Min for 10 seconds until just combined.

Add Ingredients 4 (Speculoos spread) into the Mixer bowl.

Lightly swirl into the mixture using a spoon.

Bake at 180ºC for 30-35 minutes until golden brown.

Remove from the oven, let cool in the tin.

Cut into slices and serve slightly warm.