First off, there are errors in this recipe as written. 4 Tablespoons of baking powder is way too much. The original recipe (which is what I was using, having clipped it years ago) only calls for 1 tablespoon. Also, as others have guessed, the "divided" butter quantity listed as the last ingredient in the pastry, should actually be milk.
Also, I had trouble rolling out the dough to the required size. I had to patch it a lot, but it did work, and the filling didn't leak all over the oven as I feared it might. It did start to leak a bit while still at the higher oven temp, so I put some foil on the oven rack below the pan. Lowering the temperature as specified helped it not to leak further, I'm sure.
Having said all that, we found this delicious. I did change some things from either necessity or preference.
I only had 3/4 cup shortening on hand (I use Crisco® sticks) and figured that would be plenty. It was fine. I only had 4-1/2 cups rhubarb, so I made up the difference by adding 1/2 cup frozen blueberries and 1 large apple, chopped. Probably almost any fruit would work. I really liked the way the filling came out. For the topping, I used only 1/4 cup butter and it worked out just fine. Although the pastry is not sweet at all, that sweet, crunchy topping makes all the difference.
This is one terrific pastry and I will definitely be making it again!