Preheat the oven to 375 degrees F.
In a medium bowl stir together the flour, baking powder, cinnamon, and salt. Set aside.
Place the pine nuts, 1/2 cup sugar, and fennel seeds in a food processor and pulse to mince the nuts. Add the lemon zest, lemon juice, and the carrots. Pulse to mince the carrots. Add the mascarpone cheese and pulse until the cheese is incorporated.
In a large bowl, using a hand mixer, cream together the butter and remaining 1/2 cup sugar. Add the eggs, 1 at a time, until well blended.
Add the carrot mixture to the butter mixture and stir until combined. Add in the reserved dry ingredients and stir until just incorporated.
Place the mixture in a lightly greased and floured 8 by 10 by-2-inch baking dish. Bake for 55 to 60 minutes.
Let the cake cool for 1 hour, then dust with powdered sugar. Cut into squares and serve.