Filling & Finish
1Dries: In a separate bowl, whisk together the flours and salts.
2Mixer (with paddle): Start by mixing the butter briefly on medium speed for 5 to 10 seconds. Add the brown sugar and beat together until the butter mixture is aerated and pale in color, approximately 4 minutes. Add the eggs and vanilla. Mix until it comes together into a smooth batter and the fats are homogenous.
3Add the dry ingredients all at once and mix on low speed until the dough comes together but still looks shaggy, approximately 30 seconds. Remove the bowl from the stand mixer. With a plastic bench scraper, bring the dough completely together by hand.
4Saran wrap the dough and place in refrigerator until it is chilled throughout (3 hours to overnight).
5Once chilled, remove from wrapper and scoop (with an ice cream scooper) out balls. Then roll them with your palms until you have smooth round balls.
1Combine the cornstarch with 1/4 cup of the sugar in a mixing bowl, then stir in 1/2 cup of the milk. Blend the yolks into the cornstarch mixture, stirring with a wooden spoon until completely smooth. Combine the remaining 1 1/2 cups milk with the remaining 1/2 cup sugar and the salt in a nonreactive saucepan over medium heat and bring to a boil. Remove the pan from the heat.
2Temper the egg mixture by gradually adding about 1/3 of the hot milk mixture, whisking constantly. Add the remaining milk mixture to the eggs. Return the mixture to the saucepan and continue cooking over medium heat, vigorously stirring with a whisk, until the mixture comes to a boil and the whisk leaves a trail in the pastry cream, 5-7 minutes. Remove from heat, stir in the vanilla and the butter, and cool over an ice bath. Stir occasionally until cool, about 30 minutes.
Filling & Finish
1Food Processor: Pulse the walnuts until a fine meal forms (but before their oils start releasing). Put into a bowl.
2Roll & Chill - Roll the dough into balls. Next, roll the dough balls into the nut mixture for full coverage. Chill for 20 minutes.
3Shape & Fill - Next, with a rounded tool or pestle, make an indentation into the chilled dough-balls. Next, spoon the jam into the center of each thumbprint.
4Bake on pan at a time for 8 minutes. Rotate the pan and bake until the cookies have slight cracks on the top and are set, another 6 to 8 minutes.
5When ready, the cookies will have set around the edges and be light golden brown on the bottom, but the cookies will still be soft. Let cool completely on the pan.
6To serve each cookie, take a spoonful of the custard and smear it across the jam.
7Without custard on top, the cookies can be stored in an airtight container at room temperature for up to 3 days or in an airtight container in the refrigerator for up to 1 week. Dough can be refrigerated for up to 1 week.
Mindy Segal, Cookie Love