Melt the honey, butter, and sugar in a large heavy-bottomed pan over a medium heat. Stir occasionally.
In a bowl, mix the ground spices and the salt into the flour.
Once the honey mixture has melted, set aside to cool for 10 minutes.
Once cooled a little, stir well, then whisk in the vanilla extract and egg.
Add the vinegar to the baking soda, and immediately stir into the mixture.
Gradually add the flour and spice mix to the pan, mixing well to make sure everything is incorporated, and there are no pockets of flour. You should now have a stiff dough.
Place the dough into a large bowl, cover and leave overnight in a cool place.
When you're ready to cook the pryaniki, pre-heat your oven to 325°F (170°C / gas mark 3).
Tear off small pieces of dough, and roll into walnut-sized balls.
Place onto a parchment-lined cookie sheet, leaving about 2" (5cm) between each one).
Bake in the centre of the oven for 15 minutes.
Remove from the oven, and transfer the cookies to a wire rack to cool down.
Once the gingerbread cookies are completely cool, mix together the confectioners' sugar and milk to make a smooth glaze.
Holding each cookie at the base, dip the top into the glaze, then remove, and allow the excess to drip back into the bowl. Place the cookies back on the wire rack (covered with parchment), and leave until the glaze has hardened.
Once the glaze has set, the cookies can be stored in an airtight container at room temperature for several weeks. Pryaniki can also be frozen for up to three months.