The recipe calls for instant coffee, which dissolves easily and provides a concentrated coffee flavor. However, if you prefer a stronger or milder coffee taste, you can try using espresso powder, finely ground coffee, or even brewed coffee. The amount of coffee in the recipe can be adjusted to your liking. I used 1/2 tablespoon of instant coffee dissolved in 1 tablespoon of hot water in this recipe. For a stronger coffee taste, you may add 1 to 2 tablespoons of instant coffee dissolved in 1 tablespoon of hot water, or add 1 to 1.5 tablespoons of espresso as a substitute.