Warm yogurt and stir in milk, until thoroughly mixed. Remove from heat. Add baking soda, sugar, 2 tbs butter/oleo, eggs and dry yeast. Sift together the flour and salt. Make a well in the flour and gradually add the yogurt mixture. Knead the flour 15 to 20 mins until smooth and elastic. Brush dough with some of the remaining butter/oleo. Cover with a warm, damp cloth and set aside in a warm place for 3 hours until the dough had risen to twice its size. Dust hands with flour. Knead the dough again for a few mins and divide into 8 balls. Roll each ball into a 10-in pancake. Pull each pancake gently to give it an oval shape. Cover with damp cloth 20 mins. Heat a griddle until very hot. Mix the remaining 2 tbs butter/oleo with poppy seed. Brush one side of each nan with the mixture and the other side with warm water. Place the warm-water side on the griddle for 1/2 minute. Remove from the griddle and place nan under broiler for about 2 mins. Serve with curries and tandoori dishes.