Preheat the oven to 180°C / 350°F / Gas Mark 4. Line a baking tray with parchment paper.
Combine the flour, vanilla seeds, sea salt, cream and cognac in a bowl and work together until you have a smooth ball of dough.
Add a little extra flour or cream if necessary.
Wrap the ball of dough in plastic wrap and rest it in the refrigerator for 1 hour.
Sprinkle a little flour on the work surface. Roll out the dough to a thickness of 3mm (1/8 inch). Cut out 40 circles with a 4 cm (1½ inch) cutter.
Arrange the rounds of dough on the baking tray lined with baking paper. Bake for 12–15 minutes, or until golden. Allow to cool at room temperature on the tray.
Spread half the cooled biscuits with the dulce de leche using a piping (icing) bag or a spoon.
Place the remaining biscuits on top. Press together firmly: the dulce de leche should bulge out the sides a little. Dust each alfajor with icing sugar.
Recipe and image from Argentinian Street Food, Enrique Zanoni & Gaston Stivelmaher, Murdoch Books,