Preheat the oven to 350°F (175°C).
Melt 2 teaspoons butter in the microwave, toss with 1/4 cup breadcrumbs until evenly coated, spread on a baking sheet, and bake 6–8 minutes until golden; set aside.
Cook the jumbo pasta shells according to package directions until al dente; drain and cool slightly so they are easy to handle.
Heat the marinara sauce in a medium pot over medium-low heat until warmed through, stirring occasionally.
Make the ricotta filling: whisk the egg in a small bowl, then add 2 cups ricotta and 1 cup Italian blend cheese and stir until combined.
Prepare the cream sauce: in a small pot over medium-high heat, combine 3 ounces butter and 4 ounces heavy cream; when it begins to bubble, stir in 3 ounces Parmesan until melted, then reduce heat to low and keep warm.
Spoon or pipe the ricotta mixture into each cooked jumbo shell until all 15 shells are filled.
Divide 1 cup warmed marinara among three ovenproof bowls or pie plates (about 1/3 cup each), arrange 5 stuffed shells in each dish, then pour enough cream sauce over the shells to partially cover them.
Bake the bowls in the preheated oven until heated through, about 20 minutes.
Remove from oven, sprinkle with the toasted breadcrumbs and chopped fresh parsley, and serve.