Preheat the oven to 350 degrees F.

In a food processor fitted with a steel blade attachment, pulse the graham crackers, and sugar until fine crumbs form. Add the hazelnut flour and the butter and pulse a few more times to combine. Pour the crumb mixture into a 9-inch pie plate and press crumbs into the bottom and sides of the plate using the back of a fork. Bake for 10 minutes or until lightly golden brown. Remove from the oven and cool on a wire rack.

In the meantime, mix the filling ingredients. Add the lemon zest, juice, sweetened condensed milk, egg yolks and salt to a bowl and beat with a whisk until smooth. Pour mixture into the cooled crust and bake for 15-20 minutes or until the filling is set around the edges (it will jiggle slightly in the middle). Cool at room temperature for an hour, then in the fridge for a few more, or overnight.

Before serving, beat the cream until soft peaks form. Add the powdered sugar and vanilla and continue to beat until stiff peaks form. Decoratively pipe the filling on top of the cold pie, or just dollop it on top with a spoon. Slice, serve and enjoy!