In a large bowl, dissolve the yeast in warm water. Let stand 10 minutes until bubbly. Stir in the sugar, milk, egg, salt and 3 cups flour. Dough will be shaggy. Add remaining 1/2 cup of flour onto a countertop and knead the dough 6-8 minutes, letting it absorb some of the additional flour, until smooth.
Preheat oven to 200 degrees, and then turn the oven off. Place the dough into an oiled bowl, cover with a dish towel, and place into the warm oven for 30 minutes until doubled in size.
Remove the bowl from the oven. Punch the dough down, remove it from the bowl and knead in the garlic. Form the dough into balls the size of golf balls and place them on a tray. Cover the tray with a dish towel or damp paper towel and let rise for 30 minutes.
Heat a cast iron skillet over medium-high heat. Roll out the dough and brush with melted butter. Place the buttered side down, quickly brush the top with butter and cover for 1-2 minutes, until the top is bubbling. Flip the dough over and let cook 1 more minute. Remove naan onto a plate and keep covered until ready to serve.