First, toast the nuts in a pan over a stove at medium-high heat, stirring often, until the nuts are fragrant and warm. Set aside to cool.

In a food processor, combine the nuts and about half of the granulated sugar, and pulse until a fine flour forms.

In a large bowl, whisk together the nut flour you just made, along with the all-purpose flour, the rest of the sugar, and salt.

Add the butter into the bowl, and using a pastry cutter or your hands, mix the butter into the dry ingredients until combined. Add in the vanilla and egg, and mix until a soft dough forms. It should be a bit sticky!

Lightly flour a clean, smooth surface, dump the dough onto it, and knead, adding flour, until the dough is soft and smooth without being overly sticky or gooey. Tightly wrap the dough with plastic wrap, and refrigerate for at least 1 hr.

When dough is chilled and ready, line two baking sheets with parchment or silicone liners, and form small walnut-sized balls of dough. The cookies should not spread during baking, so you can fit up to 20-25 cookies per sheet. Refrigerate the cookie dough balls for another 30 minutes before baking.

When ready, preheat the oven to 350F, and bake the cookies for 20-22 minutes. Cookies should be slightly firm to the touch but not golden.

Remove cookies to a cooling rack, and make the chocolate filling. In a microwave-safe container, combine the chocolate chips and half&half, and microwave in 20 second intervals until smooth and creamy. The half & half should thicken the mixture to be more like a cream and less like liquid chocolate.

Transfer the chocolate cream to a ziploc baggie or piping bag, cut off a small piece of a corner, and pipe the filling into the cookies, making cookie sandwiches.

Let the sandwiches stand for a few minutes to allow the filling to solidify, then enjoy!