Prepare the crust using a 9-inch pie pan or tart pan.

Rinse the blueberries and set aside to dry. In a medium-sized saucepan, whisk together the maple sugar, arrowroot starch, and cold water. Add the salt and lemon juice and whisk to combine.

Warm the mixture over medium heat, whisking continuously for 1 minute. Add 3 cups of the fresh blueberries and cook, stirring frequently, until the mixture starts to bubble and the blueberries start to pop, 3-5 minutes. Continue to cook, stirring often, until the texture starts to resemble that of blueberry jam and the liquid has thickened and started to gel slightly.

Remove the pan from the heat and stir in the remaining 2 cups of blueberries and the ghee. Pour the blueberry filling into the prebaked crust and refrigerate until set, at least 2 hours. Garnish with fresh mint, if desired, and serve.