Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line two large baking sheets with parchment/baking paper.

In a saucepan over low heat, melt the dark chocolate, heavy/double cream and butter together, until all the chocolate has fully melted.

Pour the melted chocolate mixture into a bowl, and allow it to cool until warm. Then, add the sugar, egg, vanilla and salt. Mix with a balloon whisk until the mixture becomes smooth and glossy. Set aside until needed.

In a large bowl, cream together the softened butter and light brown sugar until pale and fluffy.

Add the egg yolks and vanilla, and mix well to combine.

In a separate bowl, whisk together the gluten free flour blend, cocoa powder, xanthan gum, baking powder and salt, and add them to the wet ingredients.

Mix well until you get a smooth cookie dough with no flour clumps.

Put the granulated sugar into a small bowl.

Use a 2-tablespoon cookie or ice cream scoop to scoop out a portion of the cookie dough. Roll it between your palms to shape it into a ball, then roll it in the granulated sugar.

Place the sugar-coated cookie dough ball onto the lined baking sheet, and use a 1-tablespoon measuring spoon to make an indent in the centre.

Fill the cookies with about 1 tablespoon of the chocolate filling.

Bake the cookies at 350ºF (180ºC) for 8-9 minutes or until they've spread and puffed up slightly, and the chocolate filling is still slightly wobbly in the centre.

Allow the cookies to cool until warm on the baking sheet.

Combine the egg whites, sugar and cream of tartar in a heat-proof bowl above a pot of simmering water. Heat the meringue mixture with constant whisking until it reaches 160ºF (70ºC) and the sugar has fully dissolved.

Remove from the heat, transfer to a stand mixer and whisk for 5-7 minutes until stiff peaks form.

Pipe the Swiss meringue on the warm or room temperature cookies, then use a kitchen torch to toast it.