Cut potatoes into halves and parboil in boiling water for 10 minutes, this will ease the roasting process making them tender and crispy.
After 10minutes, drain water and transfer into a bowl. Add in the cornstarch and half portion of the melted butter and mix.
In a baking pan, add the all the ingredients and mix. Spread mixture evenly on the pan.
Transfer parboiled potatoes to the pan with the "cut" side down of the pan. This is the tip to make it super crispy.
Now put into the preheated oven bake at 400° for about 30 minutes, until they are brown and crispy on the cut surface and edges. Should be in the bottom or middle rack of the oven.
Remove from the oven, let it cool for about 3 minutes. ENJOY.