Preheat the oven to 190ºc/170ºc fan and line 2 large trays with parchment paper
Mix together the butter and sugars until creamy and combined
Add the egg and vanilla and mix through
Add the espresso powder (finely ground instant coffee) and mix through
Add the flour, bicarb, baking powder and sea salt and mix again
Split the dough into 12 - I use a 5cm scoop to make it even - and add to the trays
Chill the cookies for 30 minutes (this is optional)
Split between the two trays and bake for 11-14 minutes until deep golden
Leave to cool fully on the trays
Topping
In a new bowl, add the mascarpone cream cheese, cream, icing sugar, coffee liqueur and vanilla and whisk together
Make sure to not over whisk as it can split whilst pipping. Soft peaks is best
Using a large piping bag, pipe in circles onto the baked cookies
Dust with cocoa powder
Notes
The coffee liqueur is optional if you want the cookies to be alcohol free. If you want to increase the quantity you can, but it may make the topping hard to pipe/whip.
These cookies will last in the fridge for 3-4 days