Special equipment: 2 1/2-inch ring mold
For the bacon and tangerine dressing: Strain the tangerine juice through a mesh strainer into a small saute pan. Bring the juice to a simmer and reduce to a syrup consistency, about 5 minutes. Remove from the heat and let cool.
Heat a large saute pan over medium-high heat. Cook the bacon in a little olive oil until crispy, about 7 minutes. Transfer to paper towels to drain, reserving the fat from the pan in a small bowl.
Whisk together the mustard, 2 tablespoons of reserved bacon fat, the tangerine zest and the tangerine reduction in a small bowl.
For the crostini: Preheat a grill pan over medium-high heat. Toast the fennel seeds in a small saute pan over medium heat until fragrant, about 3 minutes, and then grind in a spice grinder. Brush both sides of the baguette slices with a little olive oil and season generously with salt, black pepper and ground fennel seed. Grill until the bread is toasted, 3 minutes per side. Remove and reserve.
For the tartar: Combine the yellowtail, parsley, capers, vinegar, mustard, chipotle puree, scallions, thyme, shallots, lemon juice and a drizzle of olive oil in a large bowl. Adjust the seasoning with salt and black pepper. Plate with the ring mold.
Drizzle some of the dressing around the plate and garnish with reserved bacon pieces. Dress the bull's blood and chervil with some of the vinaigrette, season with salt and black pepper, and use to garnish the tartar. Serve with the crostini on the side.
Bull's blood is a variety of heirloom beet, typically grown and used for its dark purple leaves.