In a small saucepan, bring sugar and ¾ cup (180 grams) water to a boil over medium-high heat, stirring until sugar is dissolved. Cook until mixture registers 248°F on a candy thermometer.
In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites and salt at medium speed until soft peaks form. Increase mixer speed to high. Pour hot sugar syrup into egg whites in a slow, steady stream, being careful to not let sugar mixture hit sides of bowl. Beat until smooth, glossy peaks form, 10 to 15 minutes. Beat in vanilla.
Recipe by Victoria at https://victoriamag.com/lord-baltimore-cake-bake-from-scratch/