Sand the tops and edges of the bottle caps, just enough to scuff them up.
Paint 2 bottle caps in the same color. Apply a thin coat. While it is still wet, sprinkle with baking soda. Immediately add more paint, dabbing to mix and apply the paint over the baking soda. Smooth out the top of the bottle cap. Make sure to apply paint to the sides too. Can gloop the baking soda and paint on to hide the ridges. Allow bottle caps to dry.
Once dry, hot glue two bottle caps of the same color with a yarn loop sticking out the top for hanging.
Then use glitter glue around the center of the two bottle caps, to hide the seam and create the macaron filling.