Peel the parsnips and thinly slice them into rounds. Blend the cream, stock and salt. Layer the parsnips, Parmesan and liquid (finishing with the Parmesan) in the ramekins.
Melt butter and add all of the topping ingredients, and gently stir until toasted. Remove thyme sprigs. Top parsnip mixture in ramekins with topping.
Cover with foil and bake at 350° F for 20 minutes. Remove foil and continue to bake for 7–10 more minutes.