Whisk the dry ingredients together in a medium/large mixing bowl.
Use your hands to rub the butter into the flour. Completely rub the butter into the dough until you have a sandy textured mixture. Add the vanilla, optional almond extract, optional salt, 20ml (1 Australian tablespoon or 4 teaspoons elsewhere) milk and 1 teaspoon oil. Use your hands to keep working the dough, squishing it through your fingers.
Continue adding milk as necessary until the dough is smooth and all pieces of flour have been picked up from the bowl. It should look and feel juicy and moist. If you squish a ball of dough in your hands, the edges should not crack as you press on it. If they do, add a teaspoon or so more milk to reach the described consistency.
Divide the dough into two even sized pieces of dough (I weigh mine). Make one piece about 30-40g larger than the other (to account for the chocolate being added).
If your kitchen is cold, you can leave the vanilla dough (the larger piece of dough) on the bench. If it's really hot, pop it in the fridge while you work on the chocolate flavour.
Melt the chocolate with the oil. Once melted, add the peppermint extract. Allow it to cool, then pour into a bowl with the smaller piece of dough. Use your hands to squelch the chocolate through the dough until is it is completely incorporated. It will feel too moist, but I promise it comes together. Place the bowl in the fridge for 10-15 minutes if you really feel it is too soft to bring together.
Take the chilled dough pieces out of the fridge. Divide each coloured piece of dough into 2 pieces (again, I like to weigh mine). Very lightly flour your work space with tapioca flour if need be (I try not to use any flour as the dough tends to be move freely without it). Use your hands to shunt the the dough into a long log of dough with a square shape. Mine was about 17cm long and 2cm x 2cm wide.
Repeat with the remaining pieces of dough, ensuring they are all pretty much the same size and length.
Place one log of chocolate dough and one log of vanilla dough next to each other on the bench. Use gentle pressure to adhere them together - you can also brush a tiny bit of milk or water between them if you like. Keep them in their square shapes as you push them together.
Brush the tops of these pieces with a tiny bit of milk or water. Place the remaining log of chocolate dough on top of the bottom log of vanilla dough. Place the remaining log of vanilla dough on top of the bottom log of chocolate dough.
Use gentle but firm pressure to adhere everything together. Press in the sides of the log and press down on the top gently. Wrap the log of dough and place it back in the fridge until thoroughly chilled. I find it easiest to make the dough the night before. You can also make this ahead and leave it in the fridge or even the freezer.