For the cookies
2/3 cup (200 g) Nutella, at room temperature
1 egg (50 g, weighed out of shell), at room temperature
3/4 cup (105 g) gum free gluten free flour (69 g superfine white rice flour + 23 g potato starch + 13 g tapioca starch/flour)
For the filling*
3 ounces bittersweet chocolate, chopped
2 tablespoons heavy whipping cream, at room temperature
*Instead of making this filling, you can: 1. Roll each cookie into a ball and then press into a disk; leave out the filling entirely; 2. Fill each hole with more Nutella before baking; or 3. press a chocolate disk or chip into the center of each cookie the moment they come out of the oven.
Preheat your oven to 350°F. Line a rimmed baking sheet with unbleached parchment paper and set it aside.
In the bowl of a food processor, place the Nutella and egg and process until smooth. Add the flour blend and and process until well-combined. The mixture will clump into a ball rather quickly. Drop the dough by the tablespoonful onto the prepared baking sheet, about 1.5-inches apart. Roll each into a ball, and replace on the baking sheet. Press a moistened index finger into the center of each ball and press all the way down.
Place in the center of the preheated oven and bake for about 9 minutes or until just set on top. Remove from the oven and allow to cool on the baking sheet until firm.
In a small bowl, place the filling ingredients and melt either in the microwave in 30-second bursts at 70% power, stirring in between until smooth, or in a double boiler. Either place the prepared filling in a pastry bag fitted with a small open piping tip and pipe into the hole of each cooled cookie, or spoon into the center of each. Allow the filling to set and serve.