PREHEAT oven to 250F. Place a rack on a baking sheet and set aside.
COOK bacon in a large frying pan over medium until crisp, 4 to 5 min. Transfer bacon to a paper-towel-lined plate. Pour bacon drippings and canola oil into a small bowl.
COMBINE celeriac, onion, eggs, flour, salt and pepper in a large bowl.
HEAT 2 tbsp oil mixture in the same frying pan over medium. Pack celeriac mixture into 1/4-cup portions, carefully turning each one into pan. Flatten into 3-in. wide fritters with a spatula. Cook until golden and crispy, 3 to 4 min per side. Transfer to prepared rack and place in oven to keep warm. Repeat with remaining celeriac mixture, adding 1 tbsp more oil mixture for each batch.
SERVE fritters topped with apple slices, sour cream, bacon and chives.
Nutrition (per piece)
Kitchen tip: Use the grate attachment on your food processor to prepare the celeriac.
Kitchen tip: If you make these without bacon, increase canola oil to 5 tbsp.