Mix the butter and sugar. Then add the flour, vanilla sugar and salt. Mix just until incorporated and place it in the freezer for about 30 minutes.
Divide the dough into 36 even pieces and place one ball of dough in the centre of each muffin form. With your fingertips, press the dough up the sides of the individual muffin tin so there is an indentation in the centre.
Place the tart pan, with the unbaked shells, in the freezer for about 10 minutes so the shortbread becomes firm. Bake until lightly browned. Once they are fully baked, remove from the oven and place on a wire rack to cool. When completely cooled, remove the tarts from the pan.
Cream filling: In your food processor or electric mixer, beat the Bonny Cream until fluffy. Add the Bonny Sweetened Condensed Milk, lemon juice, zest, and vanilla sugar and process until smooth. Transfer the filling to a bowl, cover, and refrigerate until serving time.
To serve: Using two small spoons, fill the tart shells with the cream filling. The filled tart shells can be made several hours in advance and refrigerated. Before serving the tarts, top them with cocktail cherries, fresh berries or your favourite fruits.