Seared Savoy Cabbage with Mixed Sausages

1 1 1/2 lb. Head Savoy Cabbage, Cut into 8 wedges with some core attached
1 Cup 1″ Crustless Bread Cubes
1 tsp. Mustard Powder
8 Tbsp. Olive Oil, Divided
1 Tbsp. Dijon Mustard
1 Tbsp. White Wine Vinegar
  Freshly Ground Black Pepper
2 lb. Mixed Sausages (such as sweet Italian, kielbasa, and smoked garlic
1 Tbsp. Chopped Fresh Tarragon

Bring a large pot of water to a boil over high heat. Season heavily with salt. Cook cabbage wedges until crisp-tender but not falling apart, about 5 minutes. Transfer to paper towel-lined baking sheet. Pulse bread crumbs in a food processor until coarse crumbs form; transfer to medium bowl. Add mustard powder and stir to coat.

Heat 3 Tbsp. oil in a small skillet over medium heat. Add breadcrumbs; stir frequently until golden, 4-5 minutes. Season with salt and transfer to a paper towel-lined plate to cool.

Whisk 3 Tbsp. oil, Dijon mustard, vinegar, and 1 Tbsp. water in a small bowl. Season mustard vinaigrette with salt and pepper.

Heat 1 Tbsp. oil in a large cast-iron or nonstick skillet over high heat until smoking. Working in 2 batches and adding remaining 1 Tbsp. Oil between batches, sear cabbage wedges until dark and crispy edges form on both cut sides, 3-4 minutes per side.

Cook sausages in a large skillet over medium heat until browned and cooked through (time will vary depending on whether fresh or fully cooked). Transfer cabbage to a platter; arrange sausages around. Scatter breadcrumbs and tarragon over. Serve mustard vinaigrette on the side.