Spray a square (20cm/8inch) baking tin with oil spray and line with baking paper. Then preheat the oven to 180C (350F) and place the rack in the centre of the oven.

In a medium sized heatproof bowl, melt the butter and white chocolate melts for 20 seconds in the microwave, then mix well. Continue microwaving and mixing until the butter and white chocolate has fully melted. Let cool.

Prepare the dry ingredients. In a medium sized mixing bowl, whisk the flour, baking powder, salt and mixed spice together.

Prepare the wet ingredients. In a large mixing bowl, use a stand mixer or hand mixer to beat the eggs, sugar and vanilla together until pale and light. Beat in the butter and white chocolate mixture until well incorporated.

Gently fold in the flour mixture into the wet ingredients. Fold in the orange zest, orange juice and sultanas. Then fold in the grated carrots and the white chocolate buttons. Be careful not to overmix and stop folding as soon as the ingredients come together.

In a medium sized mixing bowl, beat the cream cheese, caster sugar, egg and vanilla extract together until well mixed.

Place half of the blondie mixture into the lined tin. Then spoon half of the cream cheese mixture over the blondie mixture in the baking tin, ensuring you spread out the mixture throughout the surface of the blondie mixture. Gently place the remaining blondie mixture on top. Spoon the remaining cream cheese mixture on top and create some swirls on top using a skewer for a marbled effect. Scatter the walnuts on top. Bake for around 25-28 minutes or until a skewer comes out slightly sticky.

Let the blondies come to room temperature before cutting. Keep in an airtight container at room temperature for up to 3 days or in the fridge for up to 5 days.