For the waffles: put the flour, baking powder, sugar and salt into a mixing bowl and stir together. Put the eggs and milk into a jug with the vanilla paste, and beat together. Gradually add the liquid to the flour mixture, whisking together until smooth. Then pour in the melted butter and stir it all together. Put the waffle batter to one side for 30 minutes. Then heat up your waffle iron.
Ladle enough batter in to the waffle iron to just cover the base, then close the machine and cook for 4 minutes. Repeat until you have used up all of the batter, stacking the waffles on top of each other on a plate while you do this.
Grease the inside of one pie tin and cut out two circles of greaseproof paper - use one to line the bottom of the pie dish. Cut the second circle big enough to line the whole dish and sides, and put this to one side for later.
Cut 3 waffles in half. Position these pieces around the sides of your pie tin, then place another full waffle on the bottom to create the base.
Put the greaseproof paper on top of the waffles, then position the second pie tin on top, or inside, that - and press it down to squash the waffles together. Put a few cans or jars on top of the pie tin to weigh it down, and leave it for 30 minutes until the waffles are cool.
Preheat the oven to 180C (160C fan). Remove the weights and second pie tin from the waffle base and brush egg wash over the inside of the base - don’t brush the top of the sides of they will burn when you cook it. You just want to create a seal inside the case for when you put the filling in. Blind bake this for 15 minutes while you make the filling.
To make the filling: in a large mixing bowl, whisk together the crème fraîche, sour cream, egg, caster sugar and vanilla paste.
Remove the waffle case from the oven, and pour the cream cheese filling into it, then tip in the blueberries and use a spoon to spread them around. Bake for 30 minutes until the filling is set, then remove the pie from the oven and let it cool in the tin.
Serving the pie: once the pie has cooled, carefully remove it from the tin and put it onto a serving plate. Serve the pie the same day.