Step 1In a heavy-bottom saucepan, cook the olive oil, garlic and butter over moderate heat, whisking frequently, until the garlic just starts to color, about 7 minutes. Add the anchovies and cook, whisking, until the garlic is golden, 5 to 7 minutes more. Transfer the bagna cauda to a heatproof medium bowl and cool slightly. Whisk in the crushed red pepper and set aside until the bagna cauda is completely cooled, stirring occasionally. Season with ¾ teaspoon salt, or to taste.
Step 2Meanwhile, in a food processor, pulse the sausages until finely ground.
Step 3In a large skillet, combine the ground sausage with the water and cook over high heat, stirring frequently, until the water evaporates and the sausage is rendered, about 5 minutes. Add the canola oil and cook over moderately high heat, stirring constantly, until the sausage bits are browned and crisp, about 7 minutes more. Using a slotted spoon, transfer the crispy sausage to paper towels to drain.
Step 4In a small bowl, mix the chives with the parsley, dill and mint. In a medium bowl, whisk the Kewpie mayo with the crème fraîche, lemon juice and 1/4 cup of the mixed herbs. Season the herbed dressing with ½ teaspoon salt, or to taste.
Step 5Spread the herbed dressing in 8 very shallow bowls or on a platter. Arrange the tomatoes on top. Spoon some of the bagna cauda over the tomatoes, then sprinkle with the crispy sausage, remaining mixed herbs and fleur de sel. Serve right away.