Beat together butter and sugar until pale and fluffy.
Add the eggs, one at a time and mix well after each addition. Add the vanilla and mix well.
Add all the dried ingredients and mix until just combined.
Place scoops of cookie dough onto parchment-lined baking sheets and refrigerate for 15 minutes. I find I can comfortably get 6-8 cookies, depending on size, out of each baking sheet.
Pre-heat the oven to 180ºC/350ºF.
Bake the chilled cookie dough until cookies are golden brown and the edges are starting to firm. The centers will still feel very soft. Remove from the oven and allow to cool completely.
Dip the cooled cookies into melted white chocolate and allow to set.
Sandwich two cookies together with a scoop of vanilla ice cream and serve.