Make the tuile by combining egg whites and sugar, then add flour for a paste, and a little vanilla extract. Lay this paste onto baking sheet and spread out with a spoon. Sprinkle rustic-chopped pistachios over the flattened dough and bake at 350 until edges golden brown. This is a fragile cookie dough, don’t bake too long. Let it cool then break into large pieces.
Get the most vibrant, reddest pieces of rhubarb, and cut them into 1-inch pieces. Add them to a bowl with a little sugar, and let them macerate for about 15 mins, until the juices come out.
While that sits, cream the butter and sugar together, then add the eggs, vanilla, and milk.
In a separate bowl, whisk together flour, baking powder, and salt. Fold this in as gently as possible.
Pour the rhubarb mix into the bottom of a greased cakepan and pour the batter over the top. Bake at 350 uncovered for 35-40 mins, until lightly browned. Flip the finished cake over onto a platter. Let it cool completely.
For the semifreddo, cut a blood orange in half; juice one half and save the rest of the fruit segments. In a double-boiler on low heat, slowly heat 2 egg yolks and 1/4 cup sugar, adding 1 cup cold heavy cream a third at a time and whisking continuously until thick. Set this aside to come to room temperature.
When ready to serve, whip 1 cup heavy cream with a little blood orange juice and a little vanilla until soft peaks form. Fold this, a third at a time, into the egg mixture.
To serve, top a piece of cake with semifreddo and tuile, plus blood orange pieces and pistachio dust.