Preheat oven to 350F.
In a large bowl, beat the butter and sugars until pale and almost fluffy. Beat in the egg and vanilla.
Add the barley flour, baking soda and salt and stir or beat on low until almost combined; add the chocolate chunks and stir just until blended.
Drop dough by large spoonfuls onto a parchment-lined sheet and bake for 10-14 minutes (depending on their size) until golden around the edges but still soft in the middle. Let them set for a minute, then transfer them to a wire rack to cool.