1. Put a clean dish towel in the bottom of a large stockpot; fill halfway with water. Bring to a boil over medium heat; cover, and let simmer until ready to use.

2. Place flour, baking powder, and salt in the bowl of a food processor; pulse to combine. Add 1/2 cup butter; pulse until mixture resembles coarse meal, about 10 seconds.

3. While the machine is running, add 8 tablespoons of ice water to the mixture, and process until the dough just holds together. Wrap the dough in plastic, and refrigerate for at least 1 hour.

4. Remove two-thirds of the dough (leave remaining dough in refrigerator). Roll out to 1/8-inch thickness, and line a 1-quart pudding bowl or souffle dish with the dough.

5. Roll out the remaining dough. Layer the lined pudding bowl with half the light-brown sugar and 1/8 cup butter. Prick lemon all over with the point of a paring knife. Place lemon in center of bowl, sprinkle with remaining sugar and butter, and cover with remaining dough. Trim edges.

6. Place a 10-inch circle of waxed paper over bowl. Secure with a rubber band. Place in stockpot with towel and simmering water that comes halfway up the sides of the bowl. Cover; steam for 5 hours, making sure the water remains at a bare simmer. Add more water if necessary. Transfer from heat, and invert pudding onto a serving platter; serve immediately.