How to Make It
In a medium saucepan, warm the milk and 2/3 cup of water over low heat until it registers 82° on an instant-read thermometer. Whisk in the yeast and let stand for 15 minutes.
Whisk the butter into the yeast mixture. In a medium bowl, whisk the flour with the cornmeal and salt. Gently whisk the dry ingredients into the saucepan just until combined. Cover and let stand in a warm place for 30 minutes.
Meanwhile, in a small nonstick skillet, cook the pancetta with 1/2 cup of water over moderate heat, stirring occasionally, until all the water has evaporated, 6 to 8 minutes. Continue to cook until the pancetta is golden brown, about 2 minutes longer. Pour off all the fat in the skillet. Stir in the sauerkraut and brine and remove from the heat. Let cool.
Add the cooled pancetta mixture and the cheese to the batter and gently mix in.
Preheat the oven to 300°. Set a rack over a baking sheet and place in the oven. In a large nonstick skillet, heat 1 tablespoon of oil. In batches of 6, ladle 2 tablespoons of johnnycake batter into the skillet and cook over moderate heat, turning once, until golden and cooked through, about 3 minutes. Transfer the cakes to the rack to keep warm in the oven. Repeat with more oil and the remaining batter to make 36 johnnycakes. Serve warm, topped with crème fraîche.