Smoked Salmon and Dill Tart without eggs

700 g large jersey royal potatoes or 700 g other new potatoes 1 bunch spring onion , trimmed and sliced 300 g full-fat creme fraiche or 300 g heavy cream salt[...]

2 tablespoons white wine vinegar 1 tablespoon fresh lemon juice 1 tablespoon minced shallot 2 tablespoons chopped fresh dill 1/4 teaspoon kosher salt 1/4[...]

3 lbs baby potatoes 1 2/3 cups Greek yogurt (or sour cream) 2 garlic cloves , crushed 1 tablespoon lemon juice salt & freshly ground black pepper 1/2 cup[...]