1. Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and salt in a large bowl. Add 1 1/2 cups boiling water; stir with a wooden spoon until well combined and smooth (about 1 minute). Cover and let stand 5 minutes.
2. Scrape dough out onto a sheet of plastic wrap. Shape dough into a 2-inch-thick disk. Cut dough into 6 equal portions. Working with one dough portion at a time, place dough portion between two sheets of plastic wrap; shape into a ball, and flatten with palm of hand into a 3-inch circle (about 1/2 inch thick); shape edges to smooth.
3. Preheat oven to 350°.
4. Heat a large nonstick skillet over medium heat. Coat pan with cooking spray. Add arepas to pan; cook 5 minutes on each side or until arepa begins to brown and a crust forms. Transfer arepas to a baking sheet coated with cooking spray. Bake at 350° for 20 minutes or until arepas sound hollow when lightly tapped.
Even though both arepa flour and Mexican masa harina are precooked corn flours, arepa flour is essential to achieve the correct texture for the corn cakes. Look for arepa flour in Latin markets. Since arepa dough is slightly sticky and wet, plastic wrap makes shaping easier.