Step 1
Bring a large pot of salted water to a boil. Add 6 oz. (170 g) jumbo pasta shells and cook for 2 minutes shy of al dente according to the package directions. Drain, then spread onto a sheet pan until cool enough to handle
Step 2
Preheat oven to 350°. In a food processor, combine 2 cups (260 g) raw cashews, soaked overnight, drained, and rinsed, 1⁄2 cup (120 mL) plus 1 Tbsp. nut milk, oat milk, soy milk, or store-bought plant-based milk, 1½ Tbsp. white wine vinegar, 1½ Tbsp. nutritional yeast, 1 garlic clove, peeled, left whole, ½ tsp. onion powder, ¾ tsp. finely grated lemon zest (from ½ lemon), and ¾ tsp. flaky sea salt. Purée, scraping down the sides of the bowl if needed, until completely smooth. Use your hands to squeeze the extra liquid out of scant 1½ cups (190 g) chopped canned or jarred artichoke hearts (packed in oil or water), drained, transfer to food processor, and pulse until incorporated, about 5 pulses. You should have about 3 cups cashew ricotta. Taste and season with more salt if needed.
Step 3
Pour 1½ cups homemade or store-bought marinara sauce in the bottom of a 13×9″ baking dish with a cover. Stuff each shell with about 2 Tbsp. cashew ricotta mixture. (If you have a pastry bag, it can make the job easier. If not, use a small spoon.) Place the stuffed shells on top of the sauce. Pour remaining 1½ cups homemade or store-bought marinara sauce into the baking dish, leaving some of the cashew ricotta mixture exposed.
Step 4
Cover and bake until hot and bubbling and the pasta is completely cooked, about 30 minutes. Let sit for a few minutes, then top with chopped 3 Tbsp. finely chopped fresh parsley and serve warm.
Do Ahead: Shells can be made 3 days ahead. Store in an airtight container and refrigerate.