In a bowl, cover pecans with at least 1 inch water and let soak for 1 hour.

Meanwhile, adjust oven rack to middle position and preheat oven to 500°F (260°C). Place cauliflower on a foil-lined rimmed baking sheet, toss with olive oil, and season with salt and pepper. Roast, flipping cauliflower with a thin metal spatula halfway through roasting, until tender and deeply browned on both sides, about 20 minutes total.

In a large saucepan, melt butter over medium-high heat. Add onion, garlic, and cayenne and cook, stirring often, until softened and just starting to turn golden, about 4 minutes. Add brandy and cook until completely evaporated.

Add cauliflower, cream, and thyme. Drain pecans and add to saucepan. Bring to a simmer, then cook, adjusting heat to maintain simmer, until cauliflower has softened and liquid has reduced to about ¾ cup, about 10 minutes. Discard thyme sprig. Add soy sauce.

Using a blender or immersion blender, blend cauliflower and liquid to form a very smooth purée. Season with salt and pepper. To chill rapidly, spread vegetarian pâté in a thin, even layer on a parchment-lined baking sheet (a quarter-sheet size is best for this), then press plastic wrap directly against pâté's surface, pushing out any air. Otherwise, transfer pâté to a heatproof container and press plastic directly against surface. Refrigerate until well chilled. Transfer to a serving vessel and serve with crackers or toasted baguette rounds .