Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment.
In the bowl of a stand mixer or in a large bowl with an electric mixer, cream the butter for about 30 second, so that it is even softer. Add the sugar, vanilla, salt, baking soda and egg and beat until just combined. Add the flour and mix until smooth. Stir in the sesame seeds.
Drop the dough by tablespoonful onto the baking sheets, making sure to leave at least an inch between the wafers for spreading. Spray your hands or a spatula with nonstick spray and press the cookies down to keep them from doming.
Bake until golden brown and starting to crisp on the edges, 10 to 12 minutes. Allow the wafers to cool for 1 minute on the baking sheets, then transfer them to a wire rack to cool completely.