Homemade Custard Creams: Custard Stamps

Even after making Benjamina Ebuehi's Nutmeg Custard Cake Doughnuts, I still had some Bird's Custard Powder left. I decided to use it in Liam Charles' recipe for "Custard Stamps." They're his take on a traditional custard cream biscuit, and they are vanilla cookies made with custard powder that are sandwiched around vanilla buttercream.
The cookie batter is a mixture of softened butter, golden caster sugar (I used golden granulated sugar), egg yolk, vanilla, flour, salt, and custard powder. You chill it briefly before rolling out the dough and cutting it. I used a 2-inch square fluted cutter and I got 40 cookies from a batch, enough to make 20 sandwiches. Once the cookies are cool, you sandwich them together around an American buttercream that is a mixture of softened butter, powdered sugar, milk, and vanilla. The buttercream was quite sweet so I also added a healthy dash of salt.
The cookies had a strong vanilla flavor and I thought they were terrific. My filling was a little soft and I didn't want it to squish out when people were eating the cookies, so I put the filled cookies in the fridge to try and firm up the filling. It worked nicely, and the cookies were delicious cold, straight from the fridge. Even after a few days in the fridge, the cookies stayed crisp. These cookies were just delightful.
Recipe: "Custard Stamps" from Cheeky Treats by Liam Charles.