1 (15.25- to 16.5-ounce) package Devil's food cake mix with pudding
1/2 cup Land O Lakes® Butter, melted
1/2 cup water
1 to 2 teaspooons sea salt
1 cup Land O Lakes® Butter, softened
3 1/2 cups powdered sugar
1/3 cup prepared caramel sauce
1 teaspoon sea salt
1 teaspoon vanilla
Combine cake mix, 1/2 cup melted butter, water and eggs in bowl; beat at medium speed until smooth. Let batter rest 30 minutes.
Heat oven to 400°F.
Drop batter by slightly rounded teaspoonfuls, 2 inches apart, onto parchment-lined or lightly greased cookie sheets. Sprinkle each cookie with sea salt. Bake 5-7 minutes or until toothpick inserted in center comes out clean. Transfer to cooling rack.
Place 1 cup butter into bowl. Beat at medium speed until creamy. Add powdered sugar; beat at low speed until well mixed. Add caramel sauce, 1 teaspoon sea salt and vanilla. Beat until well mixed.
Pipe or spread rounded teaspoonful filling onto bottom of 1 cookie; place second cookie, bottom-side down over filling. Repeat with remaining cookies and filling.