Combine sugar and 1/2 c water over medium-high heat. Cook, stirring, 5-8 minutes or until sugar is dissolved. Bring to boil, then reduce heat to low and simmer for 5 minutes. Remove from heat and let stand for 5 minutes.
Stir liqueur into syrup. Refrigerate for 1 hour.
Pour syrup over mixed, cleaned berries, enough to coat. Let sit several hours, up to three days.
Serve berries by themselves or over vanilla gelato. Serve with a small amount of excess liquid, but should not be a berry soup.