Preparation / Directions:
1. To brown the butter, melt butter in a small, heavy saucepan over low heat. When fully melted, increase heat to medium and cook, stirring constantly, until the butter turns a medium brown and smells nutty. Measure out 1 cup to use for cookies and reserve the rest for the filling. Refrigerate until firm but not solid, about 30 minutes.
2. For cookies, heat oven to 325 degrees. Have ready a cookie press and ungreased baking sheet(s).
3. Beat the 1 cup brown butter, 1/2 cup of the confectioners' sugar, vanilla and salt in large bowl of electric mixer until creamy. Add egg and egg yolks and mix to combine. Stop mixer and add flour; mix on low speed just until flour disappears.
4. Transfer dough to a cookie press and press onto baking sheet in desired shapes, spacing them 1 1/2 inches apart. Bake until set, 16 to 18 minutes. Transfer to a wire rack to cool.
5. For filling, cook maple syrup in a heavy 2-quart saucepan over high heat for 5 minutes. Cool to lukewarm then stir in remaining 1/2 cup confectioners' sugar. Beat the reserved brown butter in a food processor or a small bowl of electric mixer until light. Add the syrup mixture and beat until smooth. If mixture is too thick, add a small amount of milk or cream until it is spreadable.
6. Assemble cookies by spreading about 1/2 teaspoon filling on the flat side of half the cookies. Sandwich with another coo