Combine the first 4 ingredients in a medium saucepan. Bring to a boil, stirring occasionally; remove from heat. Let stand 30 minutes.
Strain the lavender mixture through a fine sieve over a bowl, discarding the solids. Pour mixture into a 13 x 9-inch baking dish. Cover and freeze for 8 hours or until firm.
Remove the lavender mixture from freezer, and scrape entire mixture with a fork until fluffy. Garnish with lavender blooms, if desired.