In a medium bowl, pour in 1/4 cup milk and stir in the gelatin powder. Set aside for 15 minutes, allowing the gelatin to bloom.
Meanwhile, in a medium saucepan, mix together the vanilla, sugar, and the remaining 1 1/4 cup milk and salt. Heat over medium-low heat and stir until the sugar is dissolved, about 3-5 minutes. Turn off the heat.
Pour the gelatin/milk mixture into the saucepan with the milk/sugar mixture and stir until smooth, about 1 minute. Transfer to a large measuring cup (it's easier to pour later on) and allow to sit for 5 minutes, just so it cools slightly. Whisk in the kefir and mix until combined.
Divide the panna cotta between ramekins. Transfer the panna cotta to the fridge and chill until firm, at least three hours. To serve, top with berry sauce.
Combine berries, powder sugar, salt and lemon juice. Bring to a simmer on medium low heat, stirring as needed to combine and prevent sticking. Once mixture thickens like maple syrup, pour into small bowl, cover and refrigerate until serving.