Sift flour, baking powder and spices together in a large bowl and set aside.
Melt butter, sugar and treacle together in a large saucepan, then bring to the boil. Remove saucepan from heat and add bicarbonate of soda with a gentle stir. The mixture will foam and become paler in colour.
Add fresh ginger, lemon zest and vanilla paste to butter and sugar mixture with another gentle stir.
Allow to cool for 5 minutes, then mix sifted dry ingredients into the butter and sugar mixture in small batches, then egg, until smooth.
Bring the dough together into a ball, it will be warm and very soft, but do not add any flour. Flatten the dough into a disc, cover in cling film and chill for 1 hour or ideally overnight.
Preheat oven to 180°C (160°C fan-forced) and line a couple of baking trays with baking paper.
Roll dough out to a thickness of 4mm on lightly floured work surface, or between two sheets of baking paper sprinkled with flour.
Cut shapes out of dough using a round scalloped 45mm cookie cutter. For half the cookies, cut out 25mm stars. Repeat until all dough has been used.
Place cookies on a baking tray at least 1-2cm apart to allow cookies room to spread during baking. If time permits, refrigerating cookies 5-10 minutes before baking will encourage the cookies to hold their shape when baked.
Bake cookies for 7-8 minutes in the middle of the oven, until cookies are lightly browned, then remove from oven and transfer to cooling rack. Ideally bake one tray at a time to allow more evenly baked cookies.
When cookies have completely cooled, sandwich them together in pairs by piping cinnamon buttercream around the periphery and filling with salted caramel. Dust with sifted icing sugar to serve.
Beat butter, sugar, cinnamon and cloves together until very light and fluffy.
Depending on the buttercream consistency, beat in milk to slightly soften and lighten the buttercream.
Place buttercream into a piping bag fitted with a small (3-4mm) nozzle, and set aside for assembly.