How to Make It
Preheat the oven to 400°. Line a large rimmed baking sheet with parchment paper. On a lightly floured surface, roll the http://www.foodandwine.com/recipes/tender-flaky-pastry" >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.
Notes
If using fresh rhubarb, trim every bit of the leaves—they are toxic. If using frozen sliced rhubarb, thaw it slightly.