Hazelnut thumbprint cookies (kosher for Passover!)

I made these cookies last year for Passover.  That was pre-food processor, in which I attempted to pulse the whole nuts, sugar, matzah cake meal, and salt in several small batches in what I'll call a "mini-prep," a sad mini food processor wannabe.  Needless to say, they had bigger chunks of hazelnuts in them than I think the original recipe calls for.  I also made big cookies.  Big enough that I was able to use a big piece of chocolate as the center.  This time, I opted for mini cookies (by now you should not be surprised).  These are significantly smaller, and all I needed was one (upside-down) chocolate chip in the center.

The nice thing about these cookies is that they have a non-kosher for Passover (aka "regular") version, as well.  You know, for the other 357 days of the year then you don't have to use matzah cake meal.  I also think that those would be great with nutella in the center.  I mean whats better than hazelnuts and chocolate?  Hazelnuts and hazelnut-chocolate spread, I presume!

Hazelnut Chocolate Thumbprint Cookies (Thanks, SmittenKitchen!)
Makes about 24 of the Passover version (I got 45 mini ones, plus some extra dough and a lack of patience to finish making them)

1 almost-full cup (4 ounces) hazelnuts, toasted, skinned and cooled
2/3 cup sugar
2/3 cup matzo cake meal (you can substitute 1 cup plus 1 tablespoon flour)
1/4 teaspoon salt
1 stick (1/2 cup) unsalted butter, melted and cooled slightly
1 large egg, lightly beaten
1 teaspoon vanilla extract

Chocolate (I used chocolate discs last year, I stuck with chocolate chips this time around)
Pulse hazelnuts, sugar, matzo cake meal (or flour), and salt in a food processor until finely ground. (Be careful not to grind to a paste.) Transfer to a bowl and stir in butter, egg, and extract until combined well.
Chill dough, covered, until firm, about 30 minutes.
Put oven rack in middle position and preheat oven to 350°F.
Roll into 1 tbsp balls and place 1 inch apart on a parchment lined cookie sheet (you could do it on an ungreased cookie tray as well). 
Chill until slightly firm, about 10 minutes (I skipped this step).
Press one piece of chocolate firmly into the top of each ball of cookie dough and bake, 1 sheet at a time, until tops are pale golden and undersides are golden, 10 to 12 minutes (it took about 7 minutes for my mini ones).  Be careful not to overbake.
Transfer cookies to a rack and cool completely.

Smitten kitchen also has a jam-filled version and directions on how to make almond thumbprint cookies, too.  Check them out through the link above.