Step 1 Place the sugar and orange peel in a food processor bowl. Process for a minute or so, scraping down with a rubber spatula as necessary, until peel and sugar are finely blended.
Step 2 Cut the butter into pieces and process until smooth and almost fluffy. By drops, cream in one-half cup of the orange juice, then the orange liqueur, plus more drops of juice if needed. Mixture should be creamy.
Step 3Cover and refrigerate if making ahead.