Preheat the oven to 325°F convection (with the fan) or 350°F conventional (no fan). Line 12 cupcake pans with cupcake liners.

In a medium bowl, whisk together the flour, baking powder, cinnamon and salt. Set aside.

In a separate large mixing bowl, whisk the eggs until smooth. Slowly whisk in the oil to emulsify. They should be pale and voluminous.

Whisk in the granulated sugar and light brown sugar until smooth.

Fold in the flour mixture. When the dry ingredients are almost completely incorporated, then stir the carrots and chopped walnuts (if using). Fold in to distribute evenly.

Divide between the prepared muffin cups and bake in the preheated oven for 10-18 minutes or until a toothpick comes out with only a few clinging crumbs. No amount of oil, sugar, or carrots can save you from over-baking. Dryness is inevitable.

Allow to cool in pans for 2 minutes, then turn out onto a wire rack to cool completely.

While the cupcakes cool, prepare the buttercream. In a large mixing bowl with an electric mixer cream together the cream cheese, butter, and sugar until smooth.

Add lemon juice and extract. Mix well.

Place a large round piping tip (such as the Ateco 808 or 809) in a piping bag with the tip cut off. Fill with chilled buttercream (refresh in the stand mixer if it gets too stiff) and pipe a generous swirl onto the top of each cooled cupcake.