Preheat oven to 400˚F (200˚C). Grease two 10 inch (25.5 centimeter) round springform pans with butter, then line the bottom with parchment.
In a medium saucepan, place the water and 1 cup (227 grams) butter over medium heat.
In a medium bowl, combine the flour, baking powder, and salt.
Once the butter has completely melted, reduce heat to low and add the flour mixture all at once. Immediately beat with a wooden spoon or silicone spatula until fully incorporated and continue to stir until the dough lifts from the sides and bottom of the pan, about 2 minutes.
Remove the dough from heat and transfer to the bowl of a stand mixer with a paddle attachment or a large bowl. Allow to cool to room temperature.
Once the dough has cooled, beat the eggs into the dough, one at a time, until well-combined with a smooth and glossy texture.
Divide the dough into two equal pieces.
Place each piece in the prepared springform pans and spread the dough to cover the bottom, making an uneven texture with dents and waves across the surface. Do not smooth out the dough. These waves will create the mountainous shape as it bakes.
Bake both springform pans (I like to place them on baking sheets just in case any butter or moisture leaks out) in the preheated oven until puffed and golden, 20-25 minutes. Do not open the oven door until it is nearly done.
Turn off the oven and prop open the door slightly using the wooden handle of a spoon. Allow to rest for 10 minutes before removing from the oven and continuing to cool to room temperature.