Make the dough: In a food processor, combine the whole wheat flour, all-purpose flour, 1 teaspoon (5 ml / 0.2 fl oz) salt, and ajwain. With the machine running, add the 2 tablespoons (30 ml / 1 fl oz) of oil and ¾ cup of water through the feed tube. Process for 30 seconds, adding more water a little at a time, until a slightly sticky ball of dough forms.
Wrap in plastic and let it rest while you prepare the filling.
Prepare the filling: Place the potatoes in a saucepan with water to cover and a large pinch of salt.
Bring to a boil, then simmer for 15-20 minutes until tender.
Drain well. Mash the potatoes with the minced chile, ground coriander, salt, pepper, and lemon juice.
Taste and adjust the seasoning to your liking.
Divide and shape the dough: Lightly flour your work surface.
Divide the rested dough into 8 to 12 equal-sized pieces and roll each into a ball. Flatten one ball into a 2-inch disk.
Stuff the paratha: Using a floured rolling pin, roll the disk into a 5-inch round.
Place about 2 tablespoons (30 ml / 1 fl oz) of the potato filling in the center. Gather the edges of the dough up and over the filling, pinching them together to seal and form a pouch.
Roll the paratha: Gently press the sealed pouch flat into a disk. Lightly flour it and carefully roll it out into a 6 to 7-inch round.
Pat off any excess flour.
Repeat with the remaining dough and filling, stacking the rolled parathas between sheets of plastic wrap.
Cook the paratha: Heat a cast-iron skillet or griddle over medium-high heat.
Place a paratha on the hot surface and cook for about 1 minute until it darkens slightly.
Flip and cook for another 30 seconds.
Crisp it up: Brush the top surface with oil, flip, and brush the other side with oil.
Continue to cook, flipping every 30-45 seconds, until both sides are golden brown and crisp. This should take 2-3 minutes total per paratha.
Serve: Remove from the pan and brush with melted butter if serving immediately.
Enjoy warm with yogurt, pickles, or chutney.