Preheat oven to 180ºC (356ºC). Line a large flat baking tray with parchment paper, set aside.

In a large mixing bowl, using either electric hand beaters or a stand mixer with the paddle attached, add softened butter to the bowl.

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 icing sugar and vanilla. Beat with the butter for 1 minute until pale and creamy. Scraping down the sides as needed.

Sift over flour and custard powder. Beat for 30 seconds, scraping down the sides as needed. The dough will be crumbly. After the 30 seconds, turn off your beater and bring the dough together using your hands. It will stick and form a ball of dough (refer to above process shots for a visual).

To form the biscuits, pick up 2 teaspoons worth of dough, weighing 13g each. Roll into a smooth ball and place on lined tray. Leaving a small gap between each biscuit.

Take a fork and lightly press down on each biscuit, this will create that iconic yo yo appearance.

Transfer to the oven and bake for 5 minutes, then rotate the tray and bake for a further 4 minutes. They will have a hint of light golden around the edges but remain pale on top.

Remove from oven and allow to cool on tray for 10 minutes.

Transfer to a wire rack to cool completely.

In a medium sized mixing bowl, add icing sugar, melted butter and lemon juice. Use a whisk to mix it altogether until well combined, it will turn thick. Continue to whisk until smooth and no lumps of sugar remain.

Sandwich your biscuits together by pairing off 2 biscuits together. Then spoon about half a teaspoon - one teaspoon of the filling onto the bottom of one biscuit. Place the second biscuit on top and gently press together to form the sandwiched yo yo’s.

Repeat above method with remaining biscuits.

Set aside until the filling is set, about 15-30 minutes.

Serve and enjoy!