Halve potatoes and place in a large pot of cold water, covering the potatoes by at least a couple of inches. Bring to a boil over high heat, then continue boiling until potatoes are just tender.
While potatoes are boiling, crush the garlic clove in a small bowl together with the 1 tsp salt until it forms a paste. Zest lemon, then juice the lemon and measure out the 4 Tbsp. Add the zest and 4 Tbsp lemon juice to the garlic paste, then add the olive oil, mustard and some freshly ground pepper. Whisk well to combine.
When potatoes are cooked, drain and transfer to a large bowl. Immediately pour dressing on top while the potatoes are still hot and toss to combine. *There may be a pool of extra dressing at the bottom, but not to worry. It will be absorbed by the potatoes as they cool. Allow to stand at room temperature until the potatoes stop steaming. You can serve this salad warm, or cover and refrigerate. If refrigerating, remove from the fridge 15-20 minutes before serving to allow it to warm slightly, as the flavours are best when it isn't too cold. Toss with chopped chives or green onion before serving.
Be sure to read the “Ingredient and Cook's Notes" included with this recipe’s post, where I share more detailed tips, variations and substitution suggestions for this recipe!