Please let the butter soften at room temperature. To do this, you have to put them out a little earlier. Mix the horseradish, lemon juice and lemon zest with the butter and beat a little until the mixture is soft and creamy. Then stir in the rosemary and season everything with the coarse pepper and sea salt. As a small variation, you can also chop 2 - 3 small almonds and add them to the mixture.
I put the butter in a normal ice cube mold to then freeze it, but you can also form a roll with cling film or freeze the butter in any other shape.