Combine beets and potatoes in a large pot with enough water to cover them. Bring to a boil; season with sea salt and pepper. Cook for 10 minutes or until tender, then drain. Heat oil in a large skillet, and add beets and potatoes; cook for 5 minutes or until potatoes are golden brown. Reduce heat; add shallot and cook for another 3 minutes. Add cheese shreds; mix well and cook until cheese is melted, about 2 minutes. Remove from heat; add sage, walnuts, sea salt, pepper, and parmesan cheese and serve immediately.