Preheat the oven: Begin by preheating your oven to 350°F (175°C). Prepare an 8x8-inch baking dish by greasing it lightly with butter or cooking spray to prevent sticking.
Mix the wet ingredients: In a large mixing bowl, combine 1 cup grated carrots, 1/2 cup melted unsalted butter, 1 cup brown sugar, 1 large egg, and 1 tsp vanilla. Stir the mixture until it is well-combined and everything is fully incorporated.
Prepare the dry ingredients: In a separate bowl, whisk together 1.5 cups flour, 1 tsp baking powder, 1/2 tsp cinnamon, 1/4 tsp nutmeg, and 1/4 tsp salt. Ensure no lumps remain in the dry mix.
Combine both mixtures: Gradually fold the dry ingredients into the wet ingredients. Be careful not to overmix; stir until just combined, and you should see no dry flour remaining.
Spread the batter: Pour the batter into the prepared baking dish and spread it evenly with a spatula.
Bake the bars: Place the dish in the oven and bake for 25-30 minutes. You can check for doneness by inserting a toothpick into the center; it should come out clean or with a few crumbs attached.
Cool the bars: Once the bars are baked, remove them from the oven and let them cool in the baking dish for about 10 minutes. Then, transfer them to a wire rack to cool completely.
Prepare the frosting: While the bars are cooling, make the maple frosting by beating together 1/4 cup softened unsalted butter and 1/4 cup softened cream cheese until creamy. Gradually mix in 1/2 cup powdered sugar, 2 tbsp maple syrup, and 1/2 tsp vanilla until the frosting is smooth.
Frost the bars: Once the bars have cooled completely, spread the maple frosting evenly over the top. For an extra touch, sprinkle a pinch of cinnamon and some carrot shavings for garnish.
Cut and enjoy: Cut the bars into squares and serve immediately. Enjoy your delicious Carrot Bars with Maple Frosting!