How to Make It
In a blender, puree the strawberries, sugar and 1/4 cup plus 2 tablespoons of water until smooth. Scrape into a 9-by-13-inch metal baking pan and freeze overnight. Using a fork, scrape the granita until icy and flaky.
In a small bowl, whisk the gelatin with 6 tablespoons of water until smooth; let stand for 2 minutes.
In a medium saucepan, combine 2 cups of the heavy cream with the sugar and vanilla seeds and bring to a simmer, whisking to dissolve the sugar. Add the softened gelatin and cook over moderately low heat, stirring, until the gelatin is dissolved. Remove the pan from the heat and stir in the remaining 2 cups of heavy cream. Pour the panna cotta into eight 6-ounce ramekins, then cover and refrigerate until set, at least 6 hours or overnight.
In a large skillet, melt the sugar over low heat, swirling the skillet occasionally, until an amber caramel forms, 7 to 8 minutes. Add the cream and butter (the caramel will seize) and cook, stirring occasionally, until the caramel is smooth, about 5 minutes. Scrape into a heatproof bowl, stir in a pinch of salt and cool to room temperature.
Preheat the oven to 350°. Line a baking sheet with parchment paper. In a medium bowl, combine all of the ingredients, using your fingertips to blend in the butter until clumps form. Transfer to the baking sheet and bake for about 15 minutes, until golden and crisp. Transfer to a rack to cool.
To serve, invert the panna cotta onto plates. Spoon some of the caramel sauce over each panna cotta and top with some of the granita. Garnish with some of the milk crumble and serve.