Place the oreos in a food processor and blitz until they have become fine crumbs. Add the melted butter and blitz again until it is the consistency of wet sand. Alternatively, if you don't have a food processor, place the oreos in a ziplock bag and bash them violently with a rolling pin until they have become crumbs, tip into a bowl then stir in the butter.

Divide the mixture evenly between four 10cm (4 inch) loose-bottomed tart tins and press it firmly across the base and up the sides, packing it down tightly.

Place the bases in the freezer to firm up while you make the caramel.

Place the sugar and water in a heavy bottomed, light coloured saucepan. Heat, swirling the pan occasionally (don't stir), until the sugar has melted and turned amber.

Immediately remove from the heat and pour in the cream, it will bubble up ferociously. When it has calmed down slightly, add the Baileys and the butter.

Return the pan to a low heat and cook, stirring constantly, for a couple of minutes until the caramel is smooth.

Remove from the heat and add the salt, start with ⅛th tsp, taste it (very carefully!) then add more salt as needed. Allow the caramel to cool slightly (it should still be runny but not piping hot, warm is fine).

Remove the tart bases from the freezer and spread a generous tablespoon of the caramel into the base of each, return to the freezer while you make the mousse. Reserve any leftover caramel in the fridge to drizzle over the tarts before serving.

Place the chocolate and milk in a heatproof bowl over a pan of gently simmering water until the chocolate has melted, don't let the water get too hot. Stir until smooth then whisk in the egg yolk then the baileys.

Whisk the egg white in a spotlessly clean bowl until soft peaks form, gradually add the sugar while whisking and continue to whisk until it is very thick and glossy and forms stiff peaks.

Gently fold the egg white into the chocolate mixture, you may need to whisk a small amount of the white in first to loosen it.

Divide the mousse between the tart bases then place them in the fridge until the mousse has set, a couple of hours.

Line a small tray with greaseproof paper.

Place the sugar in a small, heavy bottomed, light coloured saucepan and heat, swirling the pan (not stirring), until the sugar has melted and turned caramel coloured.

Immediately remove from the heat, tip in the nuts, stir to coat then tip the mixture out onto the prepared tray. Leave until cold.

Take the tarts out of the fridge about 15 minutes before serving. Un-mould them by placing the tin on top of a small glass or jar and pressing on the rim. Gently heat the remaining caramel until it is runny (10 seconds in the microwave ought to do it) and drizzle it over the tarts.

Place the peanut brittle in a ziplock bag and bash it with a rolling pin until it has broken up into small pieces, scatter over the tarts. (Add the brittle just before serving as it will melt if kept in the fridge.)