Preheat the oven to 350°F. Line an 8x8-inch square baking pan with parchment or a reusable liner and lightly grease.
In a small saucepan or in a microwave-safe bowl, combine the butter and fresh ginger. Heat over medium-low, or microwave in 30-second increments on half-power, until just melted.
Transfer the butter mixture to a large bowl and whisk in the brown sugar, ginger syrup, ground ginger, and salt until smooth and well-combined. Add the egg and whisk until shiny and emulsified.
½ cup plus 2 tablespoons light brown sugar, ¼ cup ginger syrup* , 2 teaspoons ground ginger, 3/4 teaspoon table salt, 1 large egg
Whisk in the baking powder, then whisk in the flour and diced candied ginger until just combined. Transfer the batter to the prepared pan and spread it to reach all of the corners.
Bake the ginger bars for 15 to 20 minutes, until set in the center, then let cool slightly in the pan before transferring to a wire rack to cool completely.
Make the frosting
While the bars bake, make the frosting. Working with an electric mixer in a medium bowl or with a stand mixer fitted with the flat beater, beat the butter, cream cheese, and salt until very smooth. Add the confectioners’ sugar, vanilla, and maple syrup; beat until smooth and spreadable.
2 tablespoons unsalted butter, 2 ounces cream cheese, 1 pinch table salt, 1 ½ cups confectioners' sugar, 1 ½ teaspoons vanilla bean paste , 2 teaspoons maple syrup
Spread the frosting onto the cooled bars, then sprinkle evenly with the candied ginger. Slice and serve at room temperature.
1 tablespoon diced candied ginger
Notes
To make your own ginger syrup for baking: Slice 368g (13 ounces) fresh ginger root, unpeeled, into 1/8" or 1/4" slices (a food processor makes short work of this task. You should have about 4 cups. In a very large, heavy saucepan, bring the ginger, 3 ½ cups (695g) granulated sugar, and 3 ½ cups (794g) water to a boil. Boil the mixture for 45 to 60 minutes, until it registers 220°F on a digital thermometer. Remove the pan from the burner and carefully strain the syrup into a non-reactive container. Store ginger syrup in the refrigerator indefinitely. Yield: about 2 ¼ cups syrup.StorageStore leftover bars, well-wrapped, in the fridge for up to 5 days.If you want to make the bars ahead, I suggest baking the bars and wrapping them tightly and storing them in the fridge, unfrosted. Then, when you’re ready to serve them, make the frosting and frost the bars right before serving.