In a small bowl, whisk together 5 tablespoons custard powder and ¼ cup room-temperature milk until smooth and lump-free. Set aside.
Pour 1 litre full-fat milk into a heavy-bottom pan and bring to a rolling boil.
Lower the flame. Add ½ cup condensed milk to the boiling milk and stir to combine.
Pour in the diluted custard mixture. As soon as it's all in the pan, start stirring immediately with a spatula. Stir continuously on low flame for 4 to 5 minutes, until the custard thickens and a spatula dragged through it leaves a clear trail.
Turn off the flame and transfer the custard to a wide bowl. Let it cool completely to room temperature (about 20 to 25 minutes).
Once fully cooled, fold in ½ cup fresh mango pulp gently. The custard will turn a beautiful sunshine orange.
Trim the crusts off 9 to 12 bread slices.
In a glass rectangular tray, place a single layer of bread, fitted edge to edge. Pour over a portion of mango custard and spread evenly. Drop spoonfuls of fresh mango puree across the custard.
Repeat the layers twice more: bread, custard, mango puree dollops. Finish with a final custard layer covering everything completely.
Cover the tray and refrigerate for at least 4 hours, preferably overnight.
Just before serving, whisk together 200 ml chilled fresh cream and ¼ cup condensed milk until smooth and pourable (do not whip into peaks).
Pour the cream mixture evenly over the set pudding. Smooth the top with a spatula.
Drop 5 to 6 spoonfuls of fresh mango puree across the cream surface. Take a toothpick or the back of a spoon and drag it through the puree in long S-shapes to create the marbled swirl.
Just before serving, scatter chopped pistachios and almonds on top.
Serve chilled.