Place dates and 1/2 cup of cashews in small bowl. Pour in 1 cup boiling water and soak for 30 minutes. Meanwhile, combine remaining 3/4 cup cashews, flaxseed, and pinch of salt in a food processor and process until the mixture begins to look sandy. Add 1 tablespoon water and process until mixture begins to pull together. Form dough into a disk and place in an 8-inch square baking dish. Gently press until it forms an even layer over bottom of the dish.
Drain dates and cashews, reserving soaking liquid. Place dates and cashews in a blender. Combine soaking liquid and almond milk in a small saucepan and bring to a boil over medium-high heat; reduce heat. Stir in agar-agar and cook at a bare simmer, stirring frequently, until agar-agar is completely dissolved, 4 to 5 minutes. Pour into a blender. Add tofu, lemon zest and juice, vanilla, and remaining 1/4 teaspoon salt and blend until very smooth. Pour over dough in baking dish.
Wipe out food processor bowl and place 1 cup of raspberries in the bowl. Process until puréed. Pour purée into a fine-mesh sieve set over a small bowl. Press on mixture with the back of a spoon to extract as much purée as possible. Discard solids. Drizzle purée over top of tofu mixture. With a table knife, swirl purée into tofu mixture. Cover and refrigerate until firm, at least 4 hours. Sprinkle with remaining ½ cup raspberries, cut into squares and serve.