Wash the radicchio and either peel the leaves all the way off or give the head a rough chop. Place the leaves in a shallow pasta bowl or on a dinner plate, then peel the grapefruit, and slice the flesh (thickly enough that the slices hold their shape) and scatter it on top. Place little bites of gorgonzola around the salad. Scatter over the almonds and thyme leaves.
Mix the dressing ingredients together in a jam jar or cup (if using a jam jar, just seal and give it a really good shake to emulsify the vinaigrette) and taste. I like a very punchy, vinegar-rich dressing for this salad but if you prefer a more traditional vinaigrette, simply add a spoonful or two more olive oil until you have the consistency and flavour you like.
Drizzle the dressing on top of the salad and keep any spare for dunking bread into.