Pour sweetened condensed milk into a small saucepan; cook over low heat, stirring frequently so the milk doesn’t burn. When small bubbles form and the milk starts to cling to the pan, stir in 1 ½ cups coconut, ½ cup at a time. Stir in peanuts. Stir in vanilla extract and salt. Cook, stirring constantly, for about 4 minutes or until the mixture resembles a thick dough and no longer sticks to the bottom of the pan.