1 1/2 sticks (6 ounces) unsalted butter, at room temperature
1 1/4 cups dark brown sugar
1 large egg, at room temperature
2 cups all-purpose flour
2 teaspoons baking soda
1/2 teaspoon kosher salt
1/2 teaspoon ground ginger
1/2 teaspoon ground cinnamon
Preheat oven to 375°F.
Using an electric mixer fitted with a paddle, beat the butter and sugar until smooth and creamy. Add the egg and beat well. Scrape down the sides of the bowl.
In a separate mixing bowl, combine the flour, baking soda, salt, and spices. Add flour mixture to the butter mixture and beat until well incorporated. Scrape down the sides of the bowl and beat again.
Drop large teaspoonfuls of dough onto an unbuttered cookie sheet about 2 inches apart and bake until the edges are just brown, 8 to 12 minutes. For crispy cookies, let cool on the sheet. Let the cookie sheet cool completely between batches and repeat with the remaining dough.