from Baking:From My Home To Yours by Dorie Greenspan
For the crisp mix:
1 cup all-purpose flour
1 cup (packed) light brown sugar
3/4 cup old-fashioned oats
1/2 teaspoon ground ginger
Pinch of salt
Tiny pinch of ground cinnamon
1/2 cup finely chopped walnuts
1/4 cup very finely chopped crystallized ginger
1 stick unsalted butter, melted and cooled
For the Filling:
1 pound (4-5 medium stalks) rhubarb, trimmed and peeled
3 tablespoons cornstarch
1/2 cup cold water
3 cups strawberries, hulled and sliced
1 cup sugar
1/2 teaspoon ground ginger
1 teaspoon pure vanilla extract
Center a rack in the oven and preheat to 350ºF. Put a nonreactive 9-inch square baking pan on a baking sheet lined with parchment or a silicon mat.
Put the flour, brown sugar, oats, ground ginger, salt, and cinnamon in a large bowl and sift the ingredients through your fingers to blend them- be on the lookout for lumps in the brown sugar. Mix in the nuts and crystallized ginger, then pour over the melted butter. Using a fork, stir the ingredients until they are thoroughly moistened. Spoon half the mixture into the pan and pat it down lightly to form a thick crust. Set the remainder aside for the topping.
For the filling: Slice the rhubarb into 1/2-inch wide pieces and scatter them over the pressed in base. Dissolve the cornstarch in the cold water; set aside. Put the strawberries, sugar, and ginger in a medium saucepan and, with a fork, pastry blender, or potato masher, crush the berries. Place the pan over medium heat and, stirring occasionally, bring the mixture to a full boil. Pour the dissolved cornstarch into the pan and, stirring with a whisk, bring everything back to a boil. Keep cooking and stirring until the strawberry filling is thick and no longer cloudy, about 3 minutes. Pull the pan from the heat, stir in the vanilla, and pour the filling over the rhubarb. Scatter the remaining crisp mix over the filling, breaking it up with your fingers so you can scatter it evenly.
Slide the crisp into the oven and bake for 60 minutes, or until the topping is golden and the strawberry jam is bubbling up all around the edges. Transfer the pan to a rack and cool until only just warm or at room temperature.