Preheat the oven to 200C/400F and line a baking tray with grease proof paper/a silicone mat/Silpat.
Place flour, baking powder, bicarb, salt, sugar and cubes of butter into a large bowl. Rub the butter into the flour until you have a texture like coarse breadcrumbs.
Place double cream and 1 large egg into a jug and lightly beat until well combined and smooth.
Pour your cream mixture into the flour mixture and bring together with a fork. Continue bringing together until you have a soft dough which is slightly crumbly. Don't be tempted to knead and over work or your shortcakes won't be crumbly!
Alternatively, use your hands to bring the dough together until it's just together and there are no lumps of flour.
Halve the dough, then halve again and then again until you have 8 balls of dough. Roughly shape into 2 inch across discs/balls and place 2 inches apart on your baking tray; it's totally fine for them to not be perfect, in fact they look better being more "rustic".
Brush the top of each shortcake with beaten egg and place in the oven for 13-17 minutes, until risen, golden and an inserted skewer into the centre comes out clean. They will also feel springy to the touch.
Leave to cool on the trays whilst you make the filling: place strawberries, mango, sugar and cornflour into a medium sized saucepan and stir to coat the fruit in the cornflour.
Add in the water and place over a medium heat. Bring to a boil, stirring frequently and cook until thickened and the fruit is tender. Leave to cool for 30 mins before serving.
For the cream: place cream and icing sugar into a medium sized bowl and whisk until soft peak stage. You want it to hold its shape, but still be soft and spreadable.
Once all the elements are cool it's time to assemble! Cut a shortcake in half, spoon some of the fruit mixture onto the bottom half, top with a spoonful of cream, then place the top of the shortcake on. Then devour!!
Strawberry and Mango Shortcakes will keep without being assembled in an airtight container, for 3 days. The fruit mixture and cream mixture will keep in airtight containers in the fridge for 3 days.