Heat a 12-inch nonstick skillet over medium heat. Add one tablespoon of canola oil and one tablespoon of butter; heat until it begins to shimmer. Working in batches, drop approximately 1/4 cup of the batter into the skillet and spread the batter into 1/4-inch-thick rounds. Cook until the Boxty bottoms are golden brown, 4 to 5 minutes. Flip and cook the other side until golden brown, about 3 minutes longer. Transfer to paper towel lined plate to drain, and then to the prepared baking sheet. Keep warm in the oven while you repeat batches with more oil, butter, and batter.