Preheat oven to 350℉
Lay sliced cabbage quarters on lined baking sheet. Spray evenly with cooking spray to coat. Season with salt and pepper. Roast cabbage in oven for 40 minutes.
While cabbage bakes, prepare hot dressing.
Heat frying pan to medium heat and add bacon slices. Cook until crispy and remove to a paper towel covered plate. Let drain.
Chop bacon into rough, small pieces. (About 1/2 in size).
Drain bacon oil from skillet, reserving 1 tablespoon in pan.
Return pan to stovetop and add grain mustard. Put lid on on frying pan and let mustard seeds pop and cook for 1 minute. Add garlic and horseradish to pan, stirring to mix. Cook for 2 more minutes
Add apple cider vinegar and deglaze pan, scraping any remnants from frying pan into the vinegar as it cooks down. Cook over stovetop for 3 minutes, or until boiled down.
Lower heat to low.Add heavy cream and stir to combine.Let thicken, stirring constantly and remove pan from heat. Remove cabbage from oven, arrange on a platter.
Brush hot bacon dressing over cabbage wedges and garnish with chopped bacon and torn parsley leaves.Serve.