To make the pastry: in the bowl of a stand mixer, fitted with the beater attachment, beat the butter until smooth and soft. Stop the machine, scrape it down, and add the cornflour, egg yolk, water, salt, and sugar.
Mix again on low speed until a soft paste forms. Stop, scrape, and add flour, then mix slowly until you have a soft dough.
Flatten out into a thick disc and wrap in cling film. Chill for at least two hours, or overnight.
Cut the pastry in half and roll one half out onto a lightly floured surface in a 1/8” (3 mm) thick disc.
Use it to line an 8” or 9” tart tin.
Preheat the oven to 350°F/180°C.
Lightly prick the bottom of the pastry shell with a fork to prevent pastry from puffing up. Blind bake for 10-12 minutes. Set the baked shell aside to cool completely.
To make the filling, cook the turkey bacon in a frying pan until fat starts to render a bit. Remove the turkey bacon when done and reserve on a plate.
Next, swiftly sweat the green onions for about 1 minute only. Set aside to cool.
In a bowl, whisk together by hand the eggs, double cream, salt, pepper, cumin, and nutmeg until well combined.
Pour the egg custard mixture into the tart pan.
Arrange the turkey bacon, green onions, and tomatoes in the egg mixture in the tart pan, and then sprinkle with grated cheese.
Bake in a 350°F/180°C oven for 30 minutes or until the egg custard has completely set. Serve warm.