Combine baking soda, citric acid, corn starch, and epsom salt in a mixing bowl. Whisk till free of lumps.

Melt coconut oil in a small glass bowl in the microwave. Add the lavender essential oil and food coloring if desired.

Add the oil mixture to the dry mixture and mix well with your hands. Lightly spritz with water a couple of times to get the mixture to barely hold together. Don't add too much!

Press the mixture firmly into both halves of the bath bomb mold, overfilling them just a little. Press the halves of the mold together very firmly.

Carefully pull off the top half of the mold by gently squeezing the rim and pulling up. Flip the bath bomb over and gently remove the bottom half of the mold. If they crack or fall apart, no worries. Just start again. It took me a few tries to get it right.

Place bath bombs on a tray or pan. Let dry for at least 6 hours.