Preheat oven to 180ºC (356ºC). Line a large baking sheet with parchment paper, set aside.
Add softened butter to a large mixing bowl or the bowl of a stand mixer with the paddle attached.
Beat butter for a few seconds to break it up and it begins to turn creamy. This makes it easier on your beater when the sugar is added.
Add powdered sugar and vanilla. Beat with the butter for 1 minute until pale and creamy. Scraping down the sides as needed.
Sift over flour and cornflour. Beat for 1 minute until it turns into a soft dough. The dough will be crumbly after 30 seconds but then it will form a dough.
To form biscuits, pick up one 1/2 tablespoon of dough (15g/0.5oz) and roll it into a smooth ball.
Place on the lined baking sheet and using the back of a fork, lightly press it down to create that iconic texture.
Bake for 12-15min. They will remain pale with a light golden hint around the edges.
Remove from oven and allow to cool on sheet for 10 minutes.
Transfer to a wire rack to cool completely.
Filling
In a medium-sized mixing bowl, add powdered sugar, melted butter, milk and vanilla.
Use a whisk to mix until well combined and it turns into thick buttercream.
Sandwich your melting moments together by pairing off 2 biscuits. Then spoon about half a teaspoon - one teaspoon of filling onto the bottom of one biscuit. Place the second biscuit on top and gently press together to form the sandwich.
Repeat above method with remaining biscuits.
Set aside until the filling is set, about 15-30 minutes.
Serve and enjoy!
Notes
Make sure your butter softens to room temperature before starting.
Don't over-bake the biscuits otherwise, they won’t have that melt-in-your-mouth texture.
Store biscuits in an airtight container, at room temperature for 1 week.
To freeze, arrange them in a single layer on a baking sheet and freeze until firm. Transfer them to a freezer-safe container or bag labeled with the date and freeze for up to 3 months.
Thaw the biscuits in the fridge for a few hours or at room temperature for about 30 minutes before enjoying.