1/2 cup (1 stick) unsalted butter, room temperature, plus more for pan
2 1/2 cups all-purpose flour plus more for pan
1 cup dried tart cherries (about 6 ounces), finely chopped
1/2 cup finely chopped crystallized ginger
1 tablespoon finely grated peeled ginger
1 tablespoon Dijon mustard
1 cup hot espresso or very strong coffee
1 tablespoon ground ginger
2 teaspoons baking soda
1 1/2 teaspoons kosher salt
1 teaspoon ground allspice
1 teaspoon ground cinnamon
1/2 teaspoon freshly ground black pepper
1/2 cup (packed) dark brown sugar
3 large eggs
1 cup mild-flavored (light) molasses
Luscious Chocolate Icing (optional)