Preheat the oven to 200C (180C fan assisted, 400F).
Put the butter, sugar, eggs and vanilla in a mixing bowl. Whisk until fluffy and pale.
Sift in the flour, baking powder, salt and bicarbonate of soda. Stir until fully combined and clumpy
Gather up the pieces and knead together only as much as it takes to get a smooth ball of dough.
Wrap and place in the fridge to rest and chill for 15 minutes.
Make The Icing Toppers
Roll the sugar paste out to about 2-3mm (1/8 inch) thick. I like to work in batches so that I've got counter space.
Cut out 30 shapes using your pumpkin-shaped cookie cutter.
Place the sugar paste shapes to one side on a board lightly dusted with cornflour so that they stay flat.
Shape And Bake The Cookies
Clean your surface and dust with flour. Retrieve your chilled cookie dough and roll it out to approximately 1/2 cm (approx 1/4 inch) thick. Again, I find it it easiest to roll a 1/4-1/3 of the dough at a time so that I'm not working with too much at once.
Cut as many cookies as you can with the same pumpkin-shaped cookie cutter you used for the sugar paste. Again, aim to cut them close together to reduce the need to overwork the dough by gathering and re-rolling too many times. You should get 30 cookies in total.
Place the cookies on a lined baking sheets as you cut them out. They don't need to be spaced more than a centimetre or two (half inch) apart as they only spread a little bit.
Bake the cookies for 6 minutes or until pale golden at the edges.
Ice The Cookies
In a small container, mix the icing sugar with a teaspoon of water until dissolved to make a 'glue'.
Brush the warm cookies very sparingly with the 'glue', then place a sugar paste pumpkin on top. Repeat until all the cookies are iced.
Transfer the cookies to a cooling rack to cool and crisp up.
Add the details
Use your icing pen to add details to the pumpkin cookies. You could simply add pumpkin detail, turn them into jack-o-lanterns, or go freestyle!