For the Herbsaint Rock Sugar:
Combine Herbsaint and 1 cup sugar. Pour the mixture into a hotel pan, cover with cheese cloth, and rest at room temperature for 3 days. After 3 days, add remaining ½ cup sugar and stir. Cover again with cheesecloth, and put in a dehydrator on top of the oven. Stir once a day for 3 days, until the sugar has crystallized.
For the Strawberry Bitters Gelée:
Bring a large pot of water to a simmer. In a large bowl, combine the strawberries and sugar; cover tightly with plastic wrap. Place the bowl over the simmering water, and cook until the moisture inside the bowl creates drops of water that bead from the plastic wrap, approximately 1½ hours. Remove from the heat, and refrigerate. Do not break the plastic seal. Chill strawberries for 12 hours. Pour the strawberries into a mesh strainer, being careful not to smash the strawberries. Put a weight on top of the strawberries and drain overnight to extract all the juice. Season the juice with Peychaud's bitters. Bloom gelatin in ice cold water for 5 minutes. Remove and squeeze out excess water. Heat ½ cup strawberry juice, add gelatin, and dissolve. (The ratio for gelée is 1 cup of juice to 1.4 sheets of gelatin. Juice from strawberries will vary, so gelatin will need adjusting.) Combine the gelatin-juice mixture with additional cups strawberry juice. Cool.
For Lemon Panna Cotta:
Bloom gelatin in ice cold water for 5 minutes. Remove and squeeze out excess water. Combine cream, milk, sugar, lemon, vanilla, and salt in a pot over medium heat and scald. Remove from the heat and cool for 20 minutes. Add the buttermilk to the mixture, and stir in bloomed gelatin until dissolved. Pour through a mesh strainer. Cool and set over an ice bath to thicken slightly. Pour into ramekins and refrigerate.
To Assemble and Serve:
Spoon a dollop of the Strawberry Bitters Gelée on top of the Panna Cotta; spread to evenly coat. Top the Panna Cotta with diced strawberries, Herbsaint Rock Sugar, and a few flecks of lemon zest.