Place on parchment-lined baking paper and place in the oven at 220°C (425°F) for 15 to 20 minutes.
Salad Dressing
In a mixing bowl, mash the blue cheese slightly to make it easier to mix through.
Add the rest of the ingredients and mix well. The blue cheese does not have to be completely smooth.
Assembly
Ensure all ingredients are ready to go before grapes are roasted.
Salt is optional as the blue cheese can be salty enough.
Add everything into a mixing bowl whilst the grapes are still hot. This will help to take the bite off the arugula and soften its texture.
Gently fold so the grapes aren’t completely mashed up.
Serve immediately.
Notes
Variations And Substitutions
Milder cheese option: Not a blue cheese fan? Substitute with crumbled goat's cheese or this Whipped Feta Dressing. Both create a tangier, milder result that still works beautifully with roasted grapes and arugula.
Different leaves: If you like the anise-style flavour, endive and radicchio make great substitutes. For less bite, baby spinach leaves, mixed leaves and coral lettuce would also work well.
Different nuts: Toasted pecans are a natural swap for walnuts and slightly sweeter. Toasted pine nuts work for a more delicate crunch. For a nut-free version, substitute with pumpkin seeds (pepitas) or sunflower seeds.
Different grapes: Black grapes also roast beautifully and give a slightly deeper, more wine-like flavour. Muscat grapes are outstanding if you can find them. Intensely fragrant and sweet.
Add protein: Crumbled crispy prosciutto or pancetta scattered over the top adds a salty, savoury crunch that makes this a more substantial dish. Grilled chicken works well for a complete meal.
Make the dressing thinner: Add a splash more buttermilk if you prefer a more pourable dressing consistency. The recipe as written produces a thicker, creamier result.
How to Make This Salad Perfectly [Expert Tips]
Roast the grapes hot and fast: 220°C (425°F) is the right temperature. Any lower and the grapes will steam and become watery rather than caramelise and blister. You want the skins to split and the sugars to concentrate in 15 minutes, not slowly stew over a longer time. If at 15 minutes the skin is still taut, give it another 5 minutes.
Have everything ready before the grapes come out of the oven: This is the most important tip in the recipe. The arugula needs to be in the bowl, the dressing mixed, the walnuts ready. The moment the grapes come out of the oven is the moment assembly begins — the heat is what makes this salad special and it dissipates fast.
Do not over-mix once assembled: Fold gently rather than stirring aggressively. The roasted grapes are fragile once cooked and if you stir too vigorously they will break down completely into a purple mush throughout the salad. You want whole or half grapes with their jammy juices coating everything, not a uniformly coloured mess.
Leave the blue cheese slightly chunky: The dressing does not need to be completely smooth. Small pieces of blue cheese throughout create pockets of intense flavour as you eat. A partially mashed, slightly textured dressing is better than a completely blended one for this recipe.
Taste the dressing for salt before using: Blue cheese varies enormously in saltiness by variety and brand. Taste the dressing before pouring and the assembled salad before adding any extra salt. You may find you need none at all.
Serve the moment it is assembled: This is a warm arugula salad, so it is designed to be eaten immediately while the grapes are hot and the arugula is just wilted. It does not hold, reheat, or improve with resting. Make it, plate it, eat it.