Combine yeast and sugar in a bowl. Add ½ cup warm water. Whisk to dissolve yeast. Cover. Stand in a warm place for 10 minutes or until frothy.
Melt butter in microwave until melted. Put flour and salt into a bowl. Add Yeast mixture, yoghurt and half of the melted butter. Stir to form soft dough. Turn out onto a floured board and knead for 5 minutes or until smooth.
Place dough in a large greased bowl. Cover. Stand in a warm place for 1 hour 30 minutes or until doubled in size. Punch down dough. Turn out onto a floured surface. Knead for 5 minutes or until smooth and elastic.
Divide into 4 balls. Using a rolling pin, roll into a 20cm oval. Repeat with the remaining balls.
Using a large flat grill or large pan heat on medium high heat. Place naan on grill. Add crushed garlic to other half of butter, mix and brush onto naan. Grill for 2 minutes. Turn. Brush with the butter mixture. Grill for 2-3 minutes or until golden and puffed. Put cooked naan onto a plate covered with foil to keep warm. Repeat to cook other naan.