1 1/2 pints blackberries
1/2 cup granulated sugar
1 tablespoon cornstarch or tapioca flour
1/2 teaspoon freshly squeezed lemon juice
1 9 1/2-inch tart crust
3/4 cup all-purpose flour
1/3 cup firmly packed brown sugar
Pinch of kosher salt
3 ounces cold unsalted butter, cut into 1/2-inch pieces
1 recipe Chantilly cream (see below)
To make the streusel: In a food processor, combine the flour, brown sugar, salt, and butter and pulse until the butter is the size of large peas. Sprinkle evenly over the blackberry filling. Bake until the streusel is browned and the fruit is bubbling, about 25 minutes. Let the tart cool until it can be handled, then remove the pan sides and place on a platter. Serve warm or at room temperature, with chantilly cream on the side.
Planning ahead: The streusel made be made two days in advance, covered and refrigerated. The tart is best served the day it is made. Store at room temperature. You may reheat the tart in a 325° oven for 10 minutes.
1 cup heavy whipping cream
1/2 teaspoon vanilla extract
1 tablespoon granulated sugar
Put the cream, vanilla and sugar in a bowl and whip by hand with a whisk or with an electric mixer on medium speed until soft peaks begin to form. The cream should hold its shape but still be very smooth. Cover and refrigerate until serving.
Planning ahead: You can whip the cream an hour or two in advance, cover and refrigerate it. If it sits longer than that, it will start to thin out and you will need to rewhip it lightly before using. A few quick stirs with a whisk will do the trick.