Makes a 9''/23cm Ø nonstick round cake pan.
Sift flour with baking powder. In a stand mixer fitted with the paddle attachement, cream the softened butter with the brown sugar, salt, vanilla and almond meal on high speed until fluffy in texture, about 3 minutes then add the eggs. A standard step with the creaming method of cake preparation is to add the eggs one at a time and fully incorporate before adding the next egg. Scrap down the sides of the bowl and add sifted powders – mix until combined. Keep at room temperature.
In a medium bowl, whisk together egg yolks, vanilla, brown sugar and cornstarch. Meanwhile in a small saucepan, combine milk, sugar, lemon zest and semolina. Cook over medium heat until mixture comes to a simmer. Pour the hot milk into the egg-yolk mixture and whisk well. Pour mixture back on stove and bring to a boil whisking constantly; cook for 2 min. Turn off the heat and whisk in the hot heavy cream and add the dark rum. Transfer the custard onto a baking tray lined with plastic wrap, top with another sheet of wrap in contact and cool.
Grease cake pan generously with softened butter or cooking spray and place a disc of parchment paper on the bottom and grease it again. Pipe out a layer of batter on the bottom. Make a ring of batter around the inside perimeter of the pan. This will hold the pastry cream. Pipe pastry cream into the space. Cover with more crust. Cover the top of the cake with plastic wrap and smooth out the surface with your hand. Refrigerate until firm. Egg brush cake twice, and lightly score the top of the cake in a diamond pattern with a fork. Chill.
Bake gateau basque at 350ºF/180ºC for about 45 minutes. Let cool for 20 minutes and remove cake from the mold. Serve at room temperature. Enjoy!