Strawberry-Rhubarb Frangipane Tart

To prepare crust: Whisk spelt (or whole-wheat) flour, 3/4 cup all-purpose flour and 1/2 teaspoon salt in a large bowl. Add 8 tablespoons butter and use a pastry blender or 2 forks to incorporate it into the flour mixture until lumps the size of large peas form. Add egg and 2 tablespoons ice water and stir with a fork until the dough starts to come together. Add 1 to 2 tablespoons more water, if necessary. Transfer to a lightly floured surface and knead about 3 times to form a loose ball. Place on a piece of plastic wrap and shape into a 4-inch disk. Refrigerate the dough for at least 30 minutes or up to 1 day.

If the dough has chilled for more than 30 minutes, let it stand at room temperature for 5 minutes. Roll out on a lightly floured surface into an 11-inch circle, about 1/4 inch thick. Transfer the dough to a 9-inch tart pan with a removable bottom. Gently push out to the sides and press firmly against the fluted edges. Trim any excess dough and use it to patch any thin spots. Prick the bottom all over with a fork. Cover and freeze the tart shell for at least 30 minutes or up to 1 week.

Preheat oven to 375°F. Place the frozen tart shell on a rimmed baking sheet. Bake until light golden in the center and the edges are starting to brown, 25 to 30 minutes. Let cool on a wire rack for 30 minutes.

Meanwhile, prepare filling: Combine strawberries, rhubarb, 1/4 cup sugar, lemon zest and lemon juice in a medium saucepan. Bring to a simmer over medium-high heat. Cook, stirring frequently, until the fruit begins to break down, 3 to 5 minutes. Reduce heat to maintain a low simmer and cook, stirring occasionally, until the mixture is reduced by half, 10 to 15 minutes more. Combine water and cornstarch in a small bowl. Increase heat to medium-high and add the cornstarch mixture, whisking constantly. Cook, whisking, until the mixture comes to a boil and thickens, 2 to 4 minutes. Transfer to a bowl and let cool completely, about 1 hour.

To prepare frangipane: Combine almonds, sugar, flour and salt in a food processor. Process until the almonds are almost a powder with a bit of texture left. Add butter and pulse 3 or 4 times. Add egg and almond extract; process until well combined.

To assemble tart: Preheat oven to 350°F. Spread 1/2 cup of the strawberry-rhubarb filling in an even layer in the cooled tart shell. Spread the frangipane over it. Divide the remaining filling into 4 parallel and equidistant lines over the frangipane from edge to edge. Run the tip of a chopstick or knife through the filling perpendicular to the fruit lines from one edge of the pan to the other, then make another line 1 inch over, going in the opposite direction. Repeat to make a herringbone pattern across the whole surface.

Place the tart on a rimmed baking sheet. Bake until the frangipane is golden brown and the filling is jammy, 40 to 45 minutes. Transfer to a wire rack to cool completely, about 1 hour. Remove the pan sides. Serve at room temperature.