When one of my colleagues has a birthday, we have cake at work.
Sometimes the cake of choice is, in fact, a pie.

This recipe is based on nothing more than a basic knowledge of what makes a banoffee pie, and my failproof shortcrust pastry recipe.

Gather:
For the pastry:
250 g plain flour
125 g butter (room temperature)
1/3 cup caster sugar
1 egg yolk
20 mls cold water

For the dulce de leche filling:
1 can condensed milk (99% fat free works just fine)
A sprinkle of sea salt

To assemble:
2 ripe (but not overripe) bananas
1 cup whipping cream
200 g dark chocolate + 2 tbs extra cream (for the probably unnecessary ganache layer)
Extra dark and milk chocolate, for garnish

Then:

1. For the crust dough: Sift the flour and salt together, and add the sugar.
2. Cut the butter into cubes, and rub it into the dry ingredients until it’s sandy (or until there are no more lumps of butter). You COULD use a blender, but the fingertips method has never failed me.
3. Add the cold water and egg yolk. Mix until all the ingredients are combined, and you can form it into a single ball of dough. (Add a touch more water if it’s too dry, or a touch more flour if it’s too wet/sticky).
4. Wrap the ball in cling wrap and chill for about half an hour.
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5. For the dulce de leche filling: While the dough is chilling, pour the condensed milk into a Pyrex baking dish, sprinkle with sea salt flakes and cover with foil.*
6. Bake at about 170º C, stirring occasionally, until it starts to get thicker and more golden.
7. When the dulce de leche is about the consistency of golden syrup (or treacle), remove it from the oven. Leave the oven on, but increase the temperature to 190º C.
8. Whisk the dulce de leche, vigorously. Don’t worry if it’s a bit lumpy at first. (It will almost definitely be a bit lumpy at first.) If you whisk it enough, it WILL end up smooth. It will also thicken as it cools.
9. Set aside the dulce de leche and leave it cool to room temperature (not in the fridge, or it will set too hard to spread into the pie crust).
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10. To bake the crust: Remove the dough from the fridge, drop it into a pie tin, and press it out to form a pie crust. You COULD of course roll it out with a rolling pin but that’s messy and the fingertips method has never failed me.
11. Prick with a fork and blind bake at 190º C until dry and very slightly golden. (You could use pastry weights here, but I find the fork holes keep it from puffing up too much.)
12. Remove from oven (which you can turn off now) and leave on a cooling rack until it’s at least room temperature.
    
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13. For the perhaps unnecessary ganache layer: When the crust has cooled, melt 200 grams of dark chocolate and 2 tablespoons of cream in a double boiler (okay, a small metal bowl over a slightly smaller saucepan of boiling water).
14. Pour the chocolate mixture onto the cooled crust, and spread it out. It doesn’t need to be a thick layer (or even cover the whole base).
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15. For the whipped cream: Whip the cream. In a stand mixer (with the whisk attachment, if you have one) or with hand beaters. Not too much. If you end up with butter, that’s too much.
    
    (This is about right.)
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16. To assemble: Spoon the room-temperature dulce de leche into the pie crust and smooth it out with a palette knife. If it’s too firm, sit the bowl or container in the sun or in a bowl of warm water. (I find reheating dulce de leche too much makes it go a bit weird.)
17. Cut the bananas into quite fine slices, and layer over the dulce de leche.
    
    (Single layer + a bit of overlapping = good.)
18. Top with the whipped cream, and shaved or grated milk and dark chocolate.

Notes:
If you’re transporting the pie, I would STRONGLY advise doing it pre-assembly. Your bag will contain: the whipped cream and dulce de leche in separate containers; a block of chocolate + a grater; ‘unwrapped’ bananas; a ganache-covered baked crust. Follow steps 16–18 to assemble on arrival.

*Yes, you can boil the can instead of using the oven but make sure you google all the potential hazards beforehand. Explosions = bad. But you have to preheat the oven for the crust anyway, so why not take the safe option?