Make panna cotta: Blend strawberries, buttermilk, and sugar in a blender until very smooth. Pour through a very fine sieve into a medium bowl, pressing hard on solids and scraping the bottom of the sieve. Discard solids.
Sprinkle gelatin over milk in a small bowl and let stand 1 minute to soften.
Bring cream to a boil in a small saucepan. Remove from heat and add gelatin mixture, stirring until dissolved.
Whisk cream mixture into strawberry puree and pour into molds. Chill molds, covered, until firm, at least 8 hours.
To unmold: Dip molds in a small bowl of hot water 2 or 3 seconds, then invert onto dessert plates and remove molds. Let stand at room temperature 20 minutes to soften slightly.
Make compote while panna cottas stand: Halve strawberries lengthwise if small, or quarter if larger. Whisk together orange juice and superfine sugar in a bowl until sugar is dissolved and add strawberries, tossing to coat. Set the compote aside to macerate for 10 minutes.
Serve panna cotta with compote.
note: Panna cotta can be chilled in molds, covered, up to 2 days.