Adapted from Abigail Johnson Dodge. She makes this recipe even easier than it already is by using a food processor, but I could not find the correct attachments. So I used a pastry cutter--except it was broken! I have since ordered a new one but can also confirm that if you work quickly and use cool fingers, you can make this recipe by hand by rubbing the butter into the flour mixture, and then using 2 forks to mix the egg into the flour.
Slice the butter lengthwise and then chop into small cubes. Place in a prep bowl, cover with plastic wrap, and place the butter in the freezer while you prepare the rest of the recipe.
Place a rack in the center of the oven and preheat to 350 F. Lightly spray an 8-inch square pan with oil (to help the paper stick) and line it with parchment paper. Lightly rub a pat of butter over the parchment paper and set aside.
Whisk together the egg and vanilla and set aside.
If you are using a food processor, you can use the pulse function, but if you are working by hand, whisk together the flour, sugar, baking powder, salt and cardamom.
Sprinkle the butter over the flour mixture. Using either the food processor or a pastry cutter, cut the butter into the flour until the only clumps of butter are no bigger than peas. If using a food processor, be sure to scrape the sides and bottom of the bowl to make sure everything is being reached evenly.
Drizzle the egg mixture over the flour-butter mixture. Either using 2 forks or using the pulse function of the processor, mix until moist crumbs form. A ball of dough will NOT form.
Divide the dough in half. Press half of the dough into the prepared pan using damp fingers.
Pour the jam over the pressed in crust. Do your best to spread it evenly, and finish with a brisk shake of the pan in each direction.
Mix the chopped pistachios into the remaining dough. Then squeeze small amounts of the dough together to form small clumps. Sprinkle these over the jam--mine covered the jam nearly completely.
Bake for 36-42 minutes; a wide range is provided because some people like these bars crunchier and some like them softer. Either way, make sure the crumble top has started to get golden brown.
Let the bars cool completely before using the parchment paper to remove the "cake" from the pan. Slice into bars.
I actually liked these bars better the second day, much like shortbread, so I think they are a good option for making ahead!