The creamed fetta can be made up to a day ahead; cover and refrigerate. The vegetables can be sliced and the dressing made several hours ahead; assemble salad just before serving.
If transporting the salad, store the dressing and creamed fetta separately in airtight containers in a cooler bag. Keep refrigerated; dress salad and top with creamed fetta just before serving.
Make creamed fetta.
Slice radish, onion and cucumber thinly, using a V-slicer or mandoline, if you have one. Cut tomatoes into thick slices.
Layer radish, onion, cucumber and tomato, sprinkling each lightly with sea salt flakes, on a platter.
To make dressing, whisk oil and vinegar together in a small bowl; season to taste. Pour dressing over salad; scatter with basil.
Top salad with spoonfuls of the creamed fetta; serve with remaining creamed fetta.
Drain fetta in a fine sieve over a measuring jug to yield 1/3 cup oil; top up with a little extra virgin olive oil, if necessary. Discard any solid marinating ingredients. Coarsely crumble fetta into the bowl of a food processor; add garlic. Pulse to combine. With the motor operating, add reserved oil in a steady stream until combined (the mixture may split at this stage; the addition of milk will bring it back together). With the motor operating, slowly add milk in a steady stream until mixture is smooth and creamy. Transfer to a bowl; refrigerate until needed. The mixture will thicken on standing.
Buy a mixture of different coloured and sized tomatoes; store them at room temperature as refrigeration will dull their flavour. Use a microplane grater to grate the garlic or use a garlic press.Test Kitchen tips