Paris-Brest is a choux pastry cake of French origin, invented by Louis Durand. The cake was named after the cycling race between Paris-Brest-Paris in 1891. I am using homemade French brittle called pralin for the filling.
Pour the water into a saucepan. Add the butter, sugar and salt. Over high heat stir until the butter is melted. Bring to the boil and immediately remove from the heat. Add the flour all at once.
Mix gently at first and then more vigorously until the mixture is smooth. Return to the hob on high heat and stir until the mixture detaches from the bottom and sides of the pan but make sure not to let it scorch. When the mixture no longer sticks to the pan or the spoon, after about 30 seconds to 1 minute, remove from the hob and let cool.
In a bowl beat the eggs until foamy and gradually incorporate them into the mixture until smooth.
Fill the mixture in a pastry bag with a large round tip. Line a baking tray with greaseproof paper and pipe a thick 20cm circle on the paper. Then pipe a second much thinner circle on the paper. If both circles don't fit on the same baking tray, use a second baking tray lined with greaseproof paper. Sprinkle the thick circle with sliced almonds.
Bake for 50 to 55 minutes and do not open the oven during baking, or the pastry will collapse. If using two baking trays, bake the thicker circle on a top shelf and the thinner circle below.
It is necessary to let the air escape from the oven so that the pastry can develop its typical crust. Hold your hand in front of the oven to check if air is escaping from it. If that is not the case, you need to keep the oven door slightly open at the end of baking by wedging a wooden spoon in the door. The pastry is ready when its golden brown. Remove from the oven and let cool.
Make the pastry cream
Pulverize the brittle in a food processor. In a saucepan bring the milk to the boil and add the brittle. Whisk to combine.
In another bowl whisk the yolks with the sugar. Stir in the flour. Pour half of the boiling milk over the yolks while whisking.
Return mixture to the saucepan. Let it simmer for 30 seconds to 2 minutes while whisking constantly. The cooking time depends on the desired consistency: the more the cream cooks, the thicker it will be. Transfer the cream to a container, cover with cling film and refrigerate for 30 minutes.
Cut the thick choux pastry circle in half using a serrated knife. Fill it with half of the pastry cream.
Place the thin circle on top and cover with the remaining pastry cream. Place the top of the choux pastry with the almonds on top. Refrigerate until well chilled. If desired, dust with icing sugar before serving.