Sift baking soda, citric acid, and corn starch through a sieve into a bowl to remove larger chunks, or use a fork to mash into a fine powder.
Add in coconut or almond oil and mix well with a fork.
Fill a small spray bottle with distilled water and lightly spritz the baking-soda mixture.
Mix well until the mixture becomes the consistency of sand that can be molded with your hands.
Add lavender essential oil and mix well.
Add the mixture to the molds and allow to harden, uncovered for 3 hours, before removing.
Pop one bath bomb into your bath water and enjoy!
To Store: Store indefinitely in a covered container or jar in a cool, dark place.