Preheat the oven to 180C/350F/Gas 4. Line an 8x8-inch baking pan with aluminium foil or parchment paper, and spray with baking spray. Set aside.
Whisk together the flour, spices, and salt. Set aside.
Whisk together the butter and sugars until smooth and combined. Add the egg, egg yolk, and vanilla, and whisk vigorously until smooth and combined. Whisk in the flour until combined, then fold in the grated carrots.
Spread the batter evenly into the prepared pan, and bake for about 25 - 30 minutes, or until a toothpick inserted into the centre comes out clean. Do not over-bake. Allow to cool completely in the pan on a wire rack before frosting.
FOR THE CREAM CHEESE FROSTING
Using a handheld or stand mixer, beat the cream cheese and butter until smooth and creamy. Add half of the icing sugar, and beat until smooth. Add the vanilla, and beat until combined. Add the remaining icing sugar, and beat until light and fluffy.
Spread the frosting over the top of the blondies, sprinkle with chopped walnuts/pecans, then remove from the pan and cut into squares.
NOTES
Blondies can be stored in an airtight container at room temperature or in the fridge for up to 3 days. They also freeze well for up to 3 months. Thaw overnight the in fridge before serving.