Preheat oven to 350F. Line an 8-by-8-inch baking pan with aluminum foil, spray with cooking spray; set aside.
In a large, microwave-safe bowl melt the butter, about 1 minute on high power.
Wait momentarily before adding the egg so you don’t scramble it. Add the egg, brown sugar, vanilla, cinnamon, ginger, nutmeg, cloves, allspice, optional salt, and whisk until combined.
Add the flour and stir until just combined; don’t overmix.
Add carrots and stir to combine.
Add any optional add-ins and stir to combine.
Turn batter out into prepared pan, smoothing the top lightly with a spatula.
Bake for about 26 minutes, or until a toothpick inserted in the center comes out mostly clean, or with a few moist crumbs, but no batter.
Allow bars to cool in pan for about 30 minutes before glazing.
In a medium bowl, add confectioners’ sugar, cream cheese, butter, and whisk vigorously until smooth. As necessary, add additional sugar (if glaze seems too thin) or splash of milk (if it seems too thick) to reach desired consistency.
Optionally, add glaze to a squirt bottle and evenly glaze the bars, or simply add glaze using a spoon. Optionally, evenly spread the glaze in a thin coating over the bars, noting you will cover up the visual appeal of the carrot flecks.
