Put 2/3 of the broccoli in a large bowl with the olive oil and orange juice; season with salt and pepper and toss well to coat. Transfer the broccoli to a large rimmed baking sheet in 1 layer and roast until just tender with golden brown edges, approximately 15 minutes.
Meanwhile, pour the cream into a medium heavy-bottomed saucepan, add the remaining broccoli, garlic, and orange zest and bring to a gentle simmer over medium-low heat. Cook until the cream has reduced to half its original volume and the broccoli is cooked through, about 10 minutes.
With a hand-held immersion blender, potato masher, or food processor, blend or pulse the cream and broccoli mixture until coarsely blended and still a bit chunky. Gently fold in the roasted broccoli; taste and adjust seasoning, if necessary. Transfer to a serving bowl and serve warm.