How to Make It
In a medium bowl, stir the poppy seeds with the milk, vanilla extract and the vanilla bean. Cover the milk mixture with plastic wrap and refrigerate overnight. In another medium bowl, stir 1 1/4 cups of the granulated sugar with the vanilla seeds and cover with plastic wrap. Let stand overnight.
Preheat the oven to 375°. Grease a 10-inch bunt pan with baking spray. In a medium bowl, whisk the flour with the baking powder and salt. In a stand mixer fitted with the paddle, beat 1 1/2 sticks of the butter with the vanilla sugar and orange zest at medium-high speed until light and fluffy, about 4 minutes; scrape down the side of the bowl. Reduce the speed to medium-low and beat in the 3 whole eggs, one at a time, until incorporated, about 2 minutes. Add the dry ingredients and the wet ingredients in 3 alternating batches, beating until smooth, about 2 minutes.
Scrape the batter into the prepared pan and bake in the center of the oven for about 30 minutes, until a toothpick inserted in the center of the cake comes out clean. Transfer to a wire rack and let the cake cool in the pan for 10 minutes. Invert the cake onto the wire rack, keeping the pan on top of the cake to trap in the steam, and let cool completely, about 1 hour.
Meanwhile, in a medium saucepan, whisk the orange juice and lemon juice with the remaining 1/2 cup of granulated sugar and 3 egg yolks. Cook over moderately low heat, stirring constantly with a wooden spoon, until thickened and the custard coats the back of the spoon, about 6 minutes. Strain through a fine mesh sieve set over a medium bowl, then whisk in the remaining 4 tablespoons of butter, 1 tablespoon at time, until smooth. Let cool completely.
In a stand mixer fitted with the whisk, beat the heavy cream with the confectioners’ sugar until light and fluffy, about 3 minutes. Fold the curd into the whipped cream. Slice the cake and serve with the citrus curd whipped cream.