Make the Oreo sponge
Pre-heat your oven to 160°C/140°C fan.
Line a 2x20cm sandwich tins with greaseproof paper or reusable baking liners.
Roughly chop your Oreos (16 Oreos). I cut mine into quarters, but I don't worry if they break up a bit more. It's nice to have some larger and some smaller pieces.
Put the rest of your ingredients into a large bowl (225g self-raising flour, 2 level tsp baking powder, 225g caster sugar, 225g margarine or butter, 4 medium eggs, ¼ tsp vanilla extract).Beat, either by hand or with an electric mixer on a low speed, until the ingredients are combined and there are no lumps in the margarine/butter.Fold in the chopped Oreos.
Divide the cake mixture evenly between the prepared tins. Use the back of a spoon or spatula to spread the mixture across the tin and then level the top (it doesn't have to be perfect, just roughly even).
Bake your cakes for c. 35 minutes, until a skewer inserted into the centre comes out clean.
Once baked, remove your cakes from the oven. Leave the cakes to cool in their tins for c. 10 minutes before removing them from the tins and placing them on a wire rack to cool completely before decorating.
Make the Oreo Buttercream
Finely grind your Oreos (28 biscuits) - This is best done in a food processor so that you can grind them finely. However, you could also use a pestle and mortar or pop them into a bag and bash them with a rolling pin.
Beat your butter (160g) until soft and then gradually add the icing sugar (250g), beating in each addition before adding more.
Add the crushed Oreos and beat them into the other ingredients. You'll find that the addition of the crushed Oreos makes your buttercream quite stiff. To get the buttercream to a softer, more pipeable consistency and a little milk (1 tsp at a time), beating in each addition before adding more.
Decorate your cake
Place one sponge on your serving dish.
Spread ⅓ of the Oreo buttercream over the sponge.
Add the second sponge.
Spread ½ of the buttercream of the top.
Put the remaining buttercream into a piping bag fitted with a star nozzle (I use a JEM1B nozzle). Pipe 12 blobs of buttercream around the edge of your cake.
Add one Oreo onto each buttercream blob.
Calories: 700kcal | Carbohydrates: 87.4g | Protein: 6.9g | Fat: 35.5g | Saturated Fat: 13.6g | Fiber: 1.9g | Sugar: 58.7g
Any nutritional information provided is the estimated nutritional information per serving. Please refer to my guide to Charlotte’s Lively Kitchen nutritional information if you would like to learn more about how this is calculated.