Bring a large pot of water to a boil. Cover with a steamer basket and add the beets and potatoes.
Steam the vegetables until completely tender, 30-45 minutes. Remove from the steamer and peel once cool enough to handle.
Push the cooked beets and potatoes through a ricer or pulse in a food processor until smooth.
Place the pureed mixture in a fine mesh strainer over a bowl and set aside until cooled and any excess moisture has been drained, about 20 minutes.
While the beets and potatoes are draining, place the 2 tablespoons (30 grams) butter in a small pan over medium heat.
Once melted, stir in the breadcrumbs and cook, stirring often until golden. Set aside.
Place the drained beets and potatoes in a medium bowl. Stir in the ricotta, nutmeg, salt, and pepper.
Mix in the breadcrumbs and adjust seasonings to taste. If the filling is still too wet, add a little more breadcrumbs. Cover and refrigerate until ready to assemble.