In a small bowl, stir together evaporated milk, sugar, salt and vanilla until combined. Transfer to the container of a blender; process at medium speed for 30 seconds.
In the top of a double boiler, combine chocolate and butter. Cook over simmering water until melted; stir until smooth.
Add chocolate mixture to milk mixture; process at medium speed until thickened and smooth, 30 to 45 seconds, stopping to scrape sides of container. Transfer to a medium bowl. For a thicker consistency, frosting may be refrigerated for 15 minutes.
Recipe by Bake from Scratch at https://bakefromscratch.com/chocolate-avocado-oil-cake-chocolate-frosting/