Prepare the dough a little in advance since it must sit in the refrigerator at least 30 minutes before using. Depending on the size of your food processor you may need to divide the ingredients into 2 parts and follow the steps below for each part.

Grind the Speculoos cookies in a food processor until you have a fine crumb.

Add the flour, baking powder and brown sugar into the bowl of the food processor. Mix a couple pulses so ingredients are blended.

Cut the butter in small cubes and add to the flour mixture

Blend the butter with the flour mixture until you get a grainy texture such as cornmeal. In a food processor this usually takes about 20 seconds

Add the egg yolks into the dry mixture and mix until you get a smooth dough. In a food processor this usually takes about 30 seconds. Wait until the dough forms one piece and starts to pull away from the sides of the bowl. Remove the dough from the bowl and knead it a couple times with your hands on a clean surface with a little flour. If you are able to knead the dough without it sticking to your hands, the dough is ready. If the dough still sticks, add a little more flour until it no longer sticks.

Prepare the dough a little in advance since it must sit in the refrigerator at least 30 minutes before using.

Roll the Speculoos cookies into crumbs. Put some cookies into a Ziploc bag and lock the opening. Careful not to overstuff the bag. Use a rolling pin to roll over the Ziploc bag until you have a fine crumb. Continue until you have the amount of Speculoos crumbs that you need. You won't have as fine a result as with a food processor, but it will be sufficient. With your thumb and forefinger, break down any lumps of cookie that still remain until you have a relatively fine crumb.

Mix the flour (keep about 1/4 cup for mixing/kneading stage), baking powder, and brown sugar.

Cut the butter in small cubes and add to the flour mixture. Blend the butter with the flour mixture until you get a grainy texture such as cornmeal.

Add the egg yolks one by one into the dry mixture and mix until you get a smooth dough. If you need, add some of the reserved flour and mix some more. Continue this process (adding flour and mixing) until the dough forms one piece and starts to pull away from the sides of the bowl. Remove the dough from the bowl and knead a couple times with your hands on a clean surface with a little flour. If you are able to knead without the dough sticking to your hands, the dough is ready. If the dough still sticks, add a little more flour until it no longer sticks.

See below for common instructions for hand and food processor.

Wrap the dough in plastic wrap and put in the refrigerator at least 30 minutes. You can let this sit a few hours if you want to make ahead of time. I've used dough up to 2-3 days after it had been made.

While the dough is in the refrigerator I usually prepare the filling (see below) and preheat the oven to 175°C / 350°F

Remove the dough and start rolling out on a floured smooth surface (I use a very large cutting board). You will probably not be able to roll it out in one piece. That is ok. Try to roll it out as much as possible, keeping the thickness about a rim of a coffee cup. Put the pieces into the pie pan and press lightly. Continue until the bottom and sides are covered. I find a smooth sided pan works best (such as a pan you would use for cheesecake about 2 inches / 5 cm high with a removable bottom). When all sides are covered use the flat edge of a knife to even out the crust and smooth it over.

Put the pie tin into the oven and leave about 10 minutes until brown. I've tried to put baking paper over the crust and then fill with uncooked beans, as many suggest, but found that the sides cook before the bottom does. Try it therefore without the paper and beans. If the crust rises in parts or bubbles while cooking you can flatten it out when it comes out of the oven.

Repeat for the second pie tin.

Leave the pre-baked pie crusts to cool before filling.