Preheat oven to 375°.
To prepare muffins, place millet in a spice or coffee grinder; pulse 6 times or until lightly crushed. Set aside.
Place sugar and egg in a large bowl; beat with a mixer at medium speed until well combined. Stir in millet, buttermilk, and 1/4 cup butter.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt, stirring with a whisk. Make a well in center of mixture. Add buttermilk mixture; stir just until moist. Let batter stand 5 minutes. Spoon batter into 12 muffin cups coated with cooking spray. Bake at 375° for 18 minutes or until muffins spring back when touched lightly in center. Cool in pan 5 minutes on a wire rack. Remove muffins from pan; place on wire rack.
To prepare butter, combine 2 tablespoons butter, pecans, and honey, stirring well to combine. Serve with the muffins.