Cut out 9" round parchment paper. Place the parchment paper inside the in 9" round spring form pan and butter the sides. Run fine sugar on the sides of the pan.
In a large kitchen bowl, mix together all-purpose flour, baking powder, salt, zest from lemon, stir and set aside.
In another large bowl of a standing mixer (with paddle attachment), soften unsalted butter by beating it on medium speed (approximately 2 minutes). Reduce the speed to low and add egg yolks one at a time. Mix until eggs yolks are incorporated (it should take around another 2 minutes.) Don't over mix, the dough would be tough.
Take the sugar and stir it into the warm milk with rum in a cup. Keep the speed on low and pour this onto the softened butter in a thin stream, mixing on low speed constantly.
Gradually mix in the flour into the butter mixture. Mix on low speed, until it creates a ball of dough. Don't over mix, this should take 2 minutes maximum. Remove the ball of dough and knead gently on the floured surface, with hand until the dough is soft. Give the dough just a few kneads, so it comes easily together. The pastry dough should be soft.
Take the dough ball and wrap it in plastic food wrap and let it chill in the refrigerator for 1-2 hours. With a rolling pin, roll out the dough evenly on floured surface to 15" inch large circle. Slip the metal spatula underneath to prevent the pastry from sticking. Drape the pastry over the rolling pin and roll up halfway, so you can lift it.
Unroll the pastry over the spring form pan. Press the pastry dough gently into the bottom and up the sides of the spring form pan. Cut off the excess pastry dough with food scissors. Using fingertips, press the pastry dough into and up the sides of the pan. Refrigerate for 30 minutes.