For the cookies -

1. Line 2 baking sheets with parchment and preheat the oven to 180°C/160°C Fan/350°F (gas mark 4).
2. Gently melt the butter in a large bowl. I used the microwave but you could also do it in a pan on the hob and then tip into the bowl. Allow to cool a little.
3. Combine the flour, espresso powder, salt, baking powder and bicarbonate of soda in a medium bowl and stir well.
4. Chop the chocolate into small pieces and place in the fridge to keep it cool.
5. Add the brown sugar and caster sugar to the melted butter and stir well.
6. Now add the egg and the vanilla extract to the butter/sugar mixture and combine well.
7. Add the flour mixture and the chopped chocolate and stir until no dry ingredients remain and the chocolate is well distributed.
8. Scoop the dough into 18 portions - I find it easiest to use weighing scales for the first one and then use a dessert spoon as a guide for the remaining portions.
9. Roll the portions into balls and arrange evenly over the 2 baking sheets.
10. Bake in the preheated oven for 7-9 minutes (with my oven, 7 minutes gave the optimum soft cookie whereas 9 minutes was more attractive but crispier), until slightly golden.
11. Allow to cool completely on the baking tray and store in an airtight container.

To build the ice cream sandwiches -

1. Pop your cookies in the freezer for an hour or so before you construct them into sandwiches. The softer/chewier they are, the more important this is.
2. Use an ice cream scoop to load a cookie with ice cream. Now sandwich a second cookie on the top of the ice cream and press down gently.
3. You can enjoy them straight away or wrap in plastic or foil and freeze them for later. Avoid leaving them unwrapped in the freezer because the ice cream is a magnet for other flavours. Ugh.
4. Take them out of the freezer about 5 minutes before you want to enjoy them - of course, you don't want the ice cream to melt but the cookie needs to 'acclimatise' to life outside of the freezer.