Brussels cookies are a Pepperidge Farm's cookie product, with a mint and mini variety. They have a glossy, somewhat crunchy cookie body, well-done around the edges, with a thin layer of chocolate or mint and chocolate sandwiched in the middle depending on the style; like other Pepperidge cookies, these are marketed with a European geographical theme, here referencing the city of Brussels.
They often come in variety packs of Pepperidge Farms cookies.
References
Brussels cookies Wikipedia(Text) CC BY-SA