1. Prepare to make the ice cream by freezing the bowl of your ice cream maker overnight.
2. Heat cream, sugar, honey, and lavender buds in a saucepan over medium heat, stirring occasionally, until it comes to a very gentle boil. Immediately remove from heat and allow lavender to steep in the cream mixture, covered, for 30 minutes.
3. Pour cream mixture through a fine-mesh sieve into a bowl and discard the lavender buds.
4. Return mixture to the saucepan and heat over medium heat without bringing the mixture to a boil.
5. Whisk egg yolks in a small bowl and slowly stream 1 cup of the hot cream mixture into the bowl with the egg yolks, constantly whisking. Pour the yolk/cream mixture into the saucepan and cook over medium-low heat, stirring constantly, until thick and custardy and the mixture reaches 170°F to 175°F. Stir in the vanilla extract and sea salt.
6. Pour lavender custard through a fine-mesh sieve into a bowl and allow it to cool to room temperature, stirring occasionally.
7. Chill covered in the refrigerator for at least 3 hours.
8. Transfer lavender custard to ice cream maker and turn it on. Allow ice cream to churn until very thick. Fold in the blackberries.
9. Transfer ice cream to an airtight container and freeze at least 2 hours. Serve and enjoy!