• Heat the butter over low heat in a medium saucepan.
• Once the butter has melted, add the brown sugar, almond flour, salt, and milk.
• Cook until the ingredients are combined, stirring continuously. This should take about 3 minutes, the mixture will look a bit grainy from the almond flour, but the sugar will be dissolved.
• Remove from the heat - stir in the vanilla. The mixture will now be shiny but grainy.
• Allow the mixture to cool for at least 5-10 minutes before proceeding. It needs to thicken a bit.
• Preheat the oven to 350 degrees.
• Line several large baking sheets with parchment or silicone liners.
• Use a TEASPOON (an actual measuring spoon - not flatware) and portion out small, scant portions out onto the prepared baking sheets - placing each about 3 inches apart - they will spread a lot.
• Bake for 6-8 minutes or until golden brown around the edges. They will be bubbly on top.
• Remove and allow to cool for at least 5-10 minutes on the baking sheet before using a thin metal spatula to transfer the cookies to a wire rack to cool completely.

To assemble - gently spread a spoonful of Nutella on one cookie and top with another cookie similar in size/shape.

Sprinkle the cookies with flaky sea salt if desired.