1. Make the blue cheese dressing: Place heavy cream, 1 1/4 ounces blue cheese, brown sugar, salt, and red-pepper flakes in a medium saucepan; cook over medium-high heat, stirring, until blue cheese is melted. Remove from heat and fold in sour cream and remaining 1/2 cup crumbled blue cheese; set aside.

2. Make the Rice Krispies topping: In a medium skillet, heat butter and vinaigrette over medium heat until butter is melted. Add crisp rice cereal and toss to coat; cook until cereal is lightly toasted and fragrant. Remove from heat and set aside.

3. Make the grilled broccoli: Preheat a grill pan over medium-high heat. Place broccoli in a large bowl; add vinaigrette and toss to coat. Place broccoli on grill and cook, turning, until broccoli is charred.

4. Meanwhile, heat 1/3 cup blue cheese dressing over medium-low heat until warmed through, reserving any remaining for another use. Spread heated blue-cheese dressing on a serving plate; top with grilled broccoli. Sprinkle Rice Krispies topping over broccoli and serve.