In a large mixing bowl, beat the butter with an electric mixer until light and fluffy, about 3 minutes.
Add the parsley, red pepper flakes, black pepper, garlic, lemon zest, and the juice of half the lemon.
Mix it until fully combined, scraping down the sides of the bowl as needed.
Turn the mixture out onto a piece of plastic wrap. Using the back of a spatula, spread out the mixture into a log shape. Roll the plastic wrap up and twist the ends like a piece of candy.