Preheat the oven to 180°c (160 fan/ Gas 4/ 350F) and line 2 baking sheets with baking paper.
Cream together the butter and sugar until light and fluffy.
225 g Unsalted Butter, 100 g Golden Caster Sugar
Beat in the golden syrup, vanilla extract, and boiling water.
2 teaspoon Vanilla Extract, 1 tablespoon Golden Syrup, 1 tablespoon Boiling Water
Mix in the plain flour, baking powder, bicarbonate of soda, and rolled oats.
225 g Plain Flour, ½ teaspoon Baking Powder, ½ teaspoon Bicarbonate of Soda, 75 g Rolled Oats
Scoop heaped teaspoons of dough and roll them in your hands to form small balls. Place on the lined baking trays and flatten slightly with the palm of your hand. Bake in the oven for 15 minutes.
Beat together softened butter, vanilla extract and sieved icing sugar until you get a smooth lump-free buttercream.
75 g Salted Butter, 150 g Icing Sugar, 1 teaspoon Vanilla Extract
Once the biscuits are completely cool spread a thin layer of buttercream over the flat base of half of the biscuits and sandwich together with the remaining biscuits (so both flat bottoms of the biscuits are touching the buttercream).
Notes
Expert Tips:
The oat biscuits need to be a similar size, so try and roll the same amount of dough each time. I wouldn't go as far as telling you to weigh the dough, they just need to be roughly similar sizes so they sandwich together evenly.
It's important to line the baking sheets with nonstick baking paper or parchment paper, to prevent the biscuits from sticking to the tin.
Variations:
Make a white chocolate, milk chocolate, or dark chocolate cream cheese filling instead of using vanilla buttercream.
Replace 30g of the plain flour with cocoa powder to make chocolate gypsy cream biscuits.
Replace half the rolled oats with desiccated coconut.
Grate in the zest of 1 orange to the biscuit mixture before rolling them into balls to bake.
Eat the biscuits on their own, without the buttercream!
Storage:Store: The sandwich biscuits can be stored in an airtight container or cake tin for up to 3 days.Freeze: You can freeze the oat biscuits and vanilla buttercream separately for up to 3 months. Allow the biscuits and buttercream to thaw fully before assembling.Nutrition:The nutritional information provided is approximate and is calculated using online tools. Information can vary depending on various factors, but we have endeavoured to be as accurate as possible.