When I make this cake for guests, the aromatic flavor stumps them. Could it be cardamom, five-spice powder, or something even more exotic? They are surprised to learn the source is nothing more than fresh, ground poppy seeds.
1cup (2sticks) unsalted butter, at cool room temperature
Position a rack in the center of the oven and heat to 350°F. Using a cylinder-shaped pastry brush, butter the inside of a 9- to 9½-inch Gugelhupf mold or fluted cake pan. Coat with flour, tapping out the excess.
Beat the butter in a medium bowl using a handheld electric mixer on high speed until smooth, about 1 minute. On low speed, beat in the confectioners’ sugar. Return the speed to high and beat until the mixture is very pale and light in texture, about 3 minutes. One at a time, beat in the eggs, then the lemon zest.
Sift the flour, baking powder, and salt together into a bowl, and stir in the poppy seeds. Mix the milk, rum, and vanilla in a glass measuring cup. Stir in half of the flour, then half of the milk, then repeat. Spread evenly in the pan.
Bake until a toothpick inserted in the center of the cake comes out clean, 50 to 60 minutes. Cool on a wire rack for 10 minutes. Invert onto the rack to unmold and cool completely.