1 pound very red fresh rhubarb stalks, cut crosswise 1/2 inch thick (see
Note), or frozen sliced rhubarb
3/4 cup sugar
2 tablespoons all-purpose flour
2 teaspoons fresh lemon juice
1 teaspoon pure vanilla extract
2 tablespoons whole milk
4 tablespoons cold unsalted butter, cut into small pieces
Preheat the oven to 400°. Line a large rimmed baking sheet with parchment paper. On a lightly floured surface, roll the Tender-Flaky Pastry out to a 16-inch round 1/8 inch thick. Transfer to the baking sheet; the pastry will hang over the edges. Refrigerate the pastry for 10 minutes.
In a large bowl, toss the strawberries with the rhubarb, sugar, flour, lemon juice and vanilla. Spread on the pastry to within 2 inches of the edge. Fold the edge over the filling, pleating it at 2 inch intervals. Lightly brush the dough with the milk.
Dot the filling with the butter. Bake the galette in the center of the oven for 1 hour, or until the fruit is bubbling and the pastry is golden brown. Let the galette cool slightly before cutting into wedges.
If using fresh rhubarb, trim every bit of the leaves--they are toxic. If using frozen sliced rhubarb, thaw it slightly.