Decadent Espresso Chocolate Chip Bars

Ingredients:

1 tablespoon instant espresso powder

1 tablespoon strong brewed coffee

1 cup all-purpose flour

¼ cup unsweetened cocoa powder

½ teaspoon cream of tartar

½ teaspoon baking soda

½ teaspoon salt

¼ teaspoon ground cinnamon

½ cup unsalted butter, softened

½ cup white sugar

¼ cup firmly packed brown sugar

1 large egg, at room temperature

2 teaspoons vanilla extract

1/2 cup chocolate chips (optional)