Heat oven to 350 degrees. Butter a 13-by-9-inch glass baking pan.
Melt butter in a small saucepan over low heat. Remove from heat, add espresso and chocolate, and cover pan until chocolate is melted, about 10 minutes. In a mixing bowl, whisk the eggs, salt, sugar, bitters, cherry juice and vanilla until thick, creamy and beginning to lighten in color.
Whisk the butter and chocolate until smooth, then mix into the sugar-egg mixture just until well combined. Using a spatula, fold in the cherries, chocolate chunks and flour, using as few strokes as possible, until the flour disappears. Spread the batter evenly in the baking pan.
Bake for 30 to 45 minutes, checking after 25 minutes to avoid over-baking. When the tip of a knife inserted in the center comes out with moist crumbs, but not liquid, remove brownies from the oven. Allow to cool to room temperature, then cover and leave in the pan for several hours or overnight before cutting into squares. Store in an airtight container.