How to Make It
Preheat oven to 450ºF; line 2 large baking sheets with parchment. Place broccoli in a large bowl and drizzle with 1 tablespoon oil; sprinkle with 1/2 teaspoon each salt and pepper. Sprinkle with cayenne, if desired. Using your hands, toss to coat broccoli with oil and seasonings; spread broccoli evenly on baking sheets. Roast until broccoli is tender and lightly charred in spots, 10 to 15 minutes, stirring once and switching baking sheets from top to bottom halfway through. Let cool completely, about 20 minutes.
Meanwhile, whisk together lemon juice, mustard, and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper in a large bowl. Slowly drizzle in remaining 3 tablespoons oil, whisking constantly until blended.
Add celery, apple, and roasted broccoli to dressing; toss to coat. Top with almonds and serve.