For the first layer, cover the bottom of the trifle bowl with half the cubes of sponge or madeira cake. Make sure they are fairly snug. In the photos you can see I have made 2 layers of sponge, however that is up to you as you may get them all in one layer.
For the second layer, spoon over the 2 cans of drained fruit and spread them out evenly. Drizzle over approximately 90-100ml of the reserved syrup so it starts to seep into the sponge layer and dampen it slightly. I like to make sure I have drizzled some around the edges as visually the colour looks nice too.
Before doing the third layer, set aside 1/2 cup of the crushed Oreo cookies for decorating the top. For the third layer, halve the remaining crushed Oreo cookies, and sprinkle this over the berry layer evenly. Drizzle well with half of the Baileys Irish Cream (approximately 150ml) or more of the berry syrup for alcohol-free version - you want the Baileys to start to soak the sponge but not get it soggy.
For the fourth layer, add one of the 900g tubs of double thick custard (you can use a little less custard if you prefer - say 700g but we love custard). Dollop the custard gently and spread out evenly.
For the fifth layer, add the remaining half of sponge cubes to form a single layer. Now sprinkle over the other half of the crushed Oreo cookies (you should still have 1/2 cup reserved from before for decorating). Drizzle again with the remaining 150ml Baileys Irish Cream (approximately) or berry syrup.
For the final layer, add the other 700g- 900g double thick custard and spread out evenly (I used the chocolate flavour for this layer but you can use vanilla again).
Cover the trifle with cling wrap and refrigerate for 4 hours to allow the flavours to develop.