Add all the dressing ingredients to a screw-top jar and shake until the sugar has fully dissolved. Taste and adjust seasoning.
Add the horse gram to a pot along with 3 cups of water and salt and bring up to a boil. Turn the heat down to a low simmer and cook covered for about 30 minutes. Keep an eye on it after 30 minutes since you want it al dente and not mushy. Once cooked, drain and set aside.
Pour the dressing over the cooked horse gram whilst still hot and toss through. You may need to add more salt at this stage.
Trim and discard the dark green parts of the leeks. Chop off the bottom ends, making sure they still stay intact. Cut into long batons of about 6 inches each, and then halve them lengthwise. Rinse under running water to remove any dirt that may have accumulated inside and pat dry.
Heat butter in a large shallow pan and place the leeks cut side down and cook until lightly browned, about 2-3 minutes.
Flip them around, add the stock and honey, then cover and cook on a low flame for 10-15 minutes until soft (but still holding their shape). Once softened, turn the heat up to its maximum and cook off the remaining stock in the pan.
Plate the leeks with the lentils on top and serve warm.