Combine 1 cup butter and brown sugar in bowl. Beat at medium speed, scraping bowl often, until creamy. Add egg yolks and vanilla; continue beating until well mixed. Add flour, pecans and salt; beat at low speed until dough forms a ball.
Divide dough in half; shape each half into 10-inch long log (about 1 1/2 inches in diameter). Wrap each log tightly in plastic food wrap. Refrigerate 3 hours or overnight.
Heat oven to 350°F.
Cut each log into 1/8-inch slices with sharp knife; place 2 inches apart onto ungreased cookie sheets. Bake 7-9 minutes or until edges are lightly browned. Cool 1 minute on cookie sheet; remove to cooling rack. Cool completely.
Melt 1/4 cup butter in 2-quart saucepan over medium heat, stirring occasionally, 5-6 minutes or until butter just starts to brown. (Butter will bubble and foam. Watch closely.) Immediately remove from heat. Cool 5 minutes.
Stir in powdered sugar, vanilla and enough half & half for desired spreading consistency.
Spread 1 level teaspoon filling on bottom-side of 1 cookie; top with second cookie, bottom-side down. Squeeze together gently. Repeat with remaining cookies.
*Substitute whipping cream.
- If dough is too crumbly to easily form a log, add 1 tablespoon of very soft butter. Continue beating until dough forms a ball.
- Rather than making sandwich cookies simply frost each cookie with about 1/2 teaspoon filling mixture.