In a mixing bowl, cream together the softened butter and icing sugar until pale and creamy (2-3 minutes).
Add the vanilla extract, lemon juice, and lemon zest and beat until combined.
Add the salt, then begin gradually adding the flour with the mixer on low speed. The mixture will look very dry at first, but after a minute or two it will start to come together. Keep mixing until a soft, crumbly dough forms.
Turn the dough onto a lightly floured surface and bring it together with your hands to form a ball. Press it into a disc, then roll it out with a floured rolling pin to an even 0.6 cm (¼ in) thickness. If the dough feels soft or sticky at any point, chill it in the refrigerator for 5-10 minutes to firm up. Use a floured 5-7 cm (2-3 in) cookie cutter to cut out your desired shapes, then transfer them to a lined baking sheet and chill for 30 minutes. As the cookies chill, preheat your oven to 160℃ (140℃ fan/325℉).
Bake for about 15-18 minutes or until lightly golden around the edges. Bake times will vary depending on the size and shape of the cookies, so watch them closely from around 10 minutes. Allow to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Place the white chocolate pieces in a microwave-safe bowl and heat in 30-second intervals, stirring between each, until fully melted. If the chocolate is too thick (this will depend on the brand), stir in a neutral-flavoured oil, one tsp at a time, until it reaches a dippable consistency.
Line a baking sheet or two with parchment paper. Dip each cookie half way in the melted chocolate and allow any excess to drip off. Carefully place on the baking sheet and immediately sprinkle with chopped pistachios. Chill in the fridge until the chocolate has set.