2 cups fresh blueberries
2 cups fresh strawberries, washed, hulled, and quartered
1/4 cup granulated sugar
3 tablespoons cornstarch
1/2 teaspoon finely grated lemon zest
1 tablespoon freshly squeezed lemon juice
1/4 teaspoon vanilla extract
1/3 cup slivered almonds (about 1 1/2 ounces), finely chopped
1/4 cup all-purpose flour
1/4 cup packed dark brown sugar
1/8 teaspoon fine salt
3 tablespoons cold unsalted butter, cut into 6 pieces
Heat the oven to 375°F and arrange a rack in the middle. Line a baking sheet with parchment paper or foil; set aside.
Combine the blueberries, strawberries, granulated sugar, cornstarch, lemon zest, lemon juice, and vanilla in a large bowl and toss to coat the berries; set aside.
Whisk the almonds, flour, brown sugar, and salt in a large bowl until evenly combined. Using your hands, blend the butter pieces thoroughly into the dry ingredients until you can form the mixture into a single ball, about 2 minutes. Divide the ball into 4 equal pieces and form the pieces into patties about 2 1/2 inches wide; set aside.
Stir the berry mixture to redistribute the juices, then divide it among the jars. Place 1 almond-butter patty on top of the berries in each jar, pressing gently to compact the berries.
Evenly space the jars on the prepared baking sheet and bake until the topping is dark golden brown and crispy and the liquid is bubbling around the edges of the jar, about 30 minutes. Let cool on a rack at least 30 minutes before serving. If not serving right away, let the crisps cool to room temperature, cover, and refrigerate for up to 4 days.