Line two baking trays and preheat your oven to 180 degrees celsius (fan-forced).
Insert the Butterfly attachment and place the softened butter into the Thermomix bowl. Whip for 20 seconds, Speed 4.
Add the icing sugar and vanilla essence. Mix for a further 10 seconds, Speed 4. Scrape down the sides and mix for another 15 seconds, Speed 4.
Remove the Butterfly attachment. Add the self raising flour and custard powder to your Thermomix bowl and mix for 10 seconds, Speed 3. Scrape down the sides of the bowl with a spatula and mix for a further 15 seconds, Speed 3, or until combined.
Using a teaspoon, scoop the mixture and shape into balls before placing onto your prepared baking trays and lightly flatten with a fork - you should make around 36 biscuits.
Place the baking trays into the oven and cook for 15 minutes or until the biscuits are slightly golden on top.
Cool the melting moments on the baking trays for 5 minutes before carefully transferring to a wire rack to cool completely.
To make the lemon filling, place the softened butter, icing sugar and lemon juice into a clean Thermomix bowl. Mix for 10 seconds, Speed 6 before scraping down the sides and mixing for a further 10 seconds, Speed 6.
Spoon a little of the filling on the flat side of one biscuit before sandwiching it together with another biscuit.
Notes
RECIPE NOTES & TIPS
Soften the butter to room temperature before using
Insert the Butterfly attachment to whip the butter and to assist with mixing through the sugar
Roll the mixture into teaspoon sized balls and then press down lightly with a fork (TIP: dip the fork in flour to stop the mixture from sticking)
Bake until just lightly golden (do not overcook). The biscuits will firm slightly as they cool.
Make sure the biscuits have completely cooled before adding the icing (otherwise it will melt).
Store in an airtight container for up to 5 days.
You 'can' freeze the biscuits for up to 3 months, however, they are at their best when eaten fresh.