• In a medium bowl, combine the rhubarb and granulated sugar and toss to coat. Cover and refrigerate, stirring every hour, for 3 hours.
• Meanwhile, in a large bowl, whisk together the flours, brown sugar, and salt. Add the butter and use your hands to work it into the mixture until it has a slightly sticky and sandy texture with a mix of smaller and larger crumbles. Cover and refrigerate for at least 30 minutes, or until ready to use.
• When ready to bake, set a rack in the middle of the oven and preheat to 400°F / 200°C. Generously butter the bottom and sides of a 9-inch / 23cm square ceramic or glass baking dish.
• Using a slotted spoon, scoop the rhubarb into a medium saucepan, then add about 2 tablespoons of the liquid from the bowl (reserve the remaining liquid). Set the saucepan over low heat, cover, and cook, stirring occasionally until the rhubarb is slightly soft but not mushy, about 15 minutes. If the pan gets too dry, add more of the reserved liquid, 1 tablespoon at a time.
• Use the slotted spoon to transfer the rhubarb to a medium bowl, leaving any extra juice in the saucepan. Add the ginger to the bowl and toss gently but thoroughly with the rhubarb.
• Spread the rhubarb mixture in the prepared baking dish and sprinkle the cold crumble mixture on top. Don’t press it down. Bake until the crumble is golden, about 30 minutes.
• Set the dish on a wire rack and let the crumble cool slightly. Serve warm or cold with a side of cold rose crème anglaise or crème fraîche.

Rose Crème Anglaise

• In a small saucepan, warm the milk over low heat just until steam starts to rise from the surface; do not let it come to a simmer or bubble. Remove from the heat, then stir in the rose petals. Let the mixture steep, uncovered and at room temperature, for 30 minutes. Transfer to a small bowl, cover, and refrigerate for at least 2 hours but preferably overnight.
• Pour through a fine-mesh sieve set over a medium saucepan, pressing on the petals to extract as much flavor as possible (discard the petals). The milk will be a very light brown color. Add the salt and set the pan over low heat to warm just until steam starts to rise from the surface; do not let it come to a simmer or bubble.
• Meanwhile, in a heatproof medium bowl, vigorously whisk the egg yolks and the sugar until fully combined and lighter in color.
• Remove the hot milk from the heat and while stirring constantly with a wooden spoon, very gradually add it to the egg yolk mixture. Pour the mixture back into the saucepan, set it over medium-low heat, and warm it, stirring frequently, until the small bubbles disappear and the mixture thickens and becomes opaque on the spoon. Do not let it boil. One way to know if it’s ready is to coat your spoon with the mixture and run your finger over it. If the line is neat, then it’s ready. A more precise way to know is if the mixture is about 185°F / 85°C. It will thicken as it sits.
• Pour through a fine-mesh sieve set over a serving bowl and let stand at room temperature for 20 minutes, stirring every 5 minutes to prevent a skin from forming. You will end up with a light brown cream. Cover and refrigerate until cold, about 1 hour. Whisk before serving and sprinkle with dried rose petals for decoration. The crème anglaise keeps in an airtight container in the refrigerator for up to 2 days. Make sure to whisk it before serving.