Prepare the tomatoes: Wash and dry your heirloom tomatoes. Cut the larger ones into wedges about the size of a thumb, halve or quarter the medium ones, and leave the smallest cherry-sized ones whole. As you work, you should see the vibrant colours — deep crimson, sunshine yellow, striped green — and smell that sweet, earthy, sun-warmed tomato aroma.

Slice the onion: Peel the red onion and slice it as thinly as you possibly can, ideally using a mandoline or a very sharp knife. The slices should be almost translucent, so they soften in the dressing rather than overpowering the salad with raw bite. You'll see the purple rings separate naturally as you go.

Prepare the basil: Stack the basil leaves on top of each other, roll them tightly into a cigar shape, and slice crosswise into thin ribbons (this is called a chiffonade). You should see the bright green edges release a burst of peppery, anise-like fragrance as the knife cuts through.

Make the dressing: In a small jar with a tight-fitting lid, combine the extra virgin olive oil, balsamic vinegar, grated garlic, Dijon mustard, flaky sea salt, and black pepper. Screw the lid on tightly and shake vigorously for about 20 seconds until the dressing looks thick and emulsified, with no visible separation of oil and vinegar.

Assemble the salad: Place the prepared tomatoes and sliced red onion in a large salad bowl. Pour the dressing over the top and toss gently with your hands or salad servers, being careful not to crush the tender tomato wedges. You'll see the dressing coat every piece in a glossy, translucent sheen.

Rest and chill: Cover the bowl with cling film or a clean tea towel and let it sit at room temperature for at least 30 minutes. This resting time is crucial — the salt draws moisture from the tomatoes, creating a light, flavourful juice that mingles with the dressing. You'll notice a pool of ruby-coloured liquid forming at the bottom of the bowl.

Finish and serve: Just before serving, scatter the basil ribbons over the top. If you're using mozzarella pearls or burrata, tear them into pieces and arrange them among the tomatoes. Give everything one final gentle toss, taste for seasoning — you might want an extra pinch of salt — and serve immediately while still nicely chilled.