Giant Salted Hot Fudge Cookies with Coffee Salt

Name: Giant Salted Hot Fudge Cookies with Coffee Salt
Prep time: 1 h 15 min
Cook time: 15 min
Total time: 1 h 30 min
Cuisine: American
Ingredients: 1/4 cup unsweetened cocoa powder; 2/3 cup whole milk; 3/4 cups semi-sweet chocolate chips; 5 ounces chopped dark chocolate or 3/4 cup additional chocolate chips ((I use 70% dark)); 2 tablespoons salted butter, cubed; 1 teaspoon vanilla extract; 2 sticks (1 cup) salted butter, at room temperature; 3/4 cup dark brown sugar; 1/4 cup granulated sugar ((use 1/2 cup for a sweeter cookie)); 2 large eggs, at room temperature; 2 teaspoons vanilla extract; 2 1/4 cups all-purpose flour ((+2 tablespoons, if needed, see note)); 1 teaspoon baking soda; 1 tablespoon flaky sea salt; 1 tablespoon instant coffee powder ((optional))