Whisk together gelatin and ¹⁄₄ cup water in a bowl until there are no lumps and set aside for at least 10 minutes to bloom. Meanwhile, in a medium-sized pot, combine cream, sugar, vanilla, and lavender, and simmer over a medium-low heat until sugar is dissolved and fragrant. You should see steam coming off the top. Ladle a little hot cream into the bloomed gelatin and whisk until no lumps. Add back into the pot and whisk together to incorporate all the gelatin into the cream. Add a pinch of salt and coloring (optional). Strain the mixture and pour into serving vessels. Cover and cool for four hours, or preferably overnight until completely set. In a small pot, whisk together lemon juice, water, sugar, and cornstarch, and heat over low heat until thickened. If too thick, thin with a little more lemon juice. Cool completely. Pour enough coulis to just cover the top of the panna cotta, and serve with a small dollop of whipped cream. Enjoy!