The next time you need an egg substitute in baking, try making a flax "egg." It's made with a simple combination of ground flax seed and water, or you can use chia seeds, too. I've been using these for over a decade, so I'll share what I've learned below-- including when flax seeds won't work in a recipe.
Add the ground flaxseed and water to a bowl and stir until well combined. Let the mixture rest for at least 5 minutes to allow it to thicken. Note: If using this in a quick bread recipe, use only two tablespoons of water, rather than 3. Breads and cakes don't need the extra moisture. If you don't want soft cookies, you can use just 2 tablespoons in that case as well.
When the flax egg looks thicker, you can use it as an egg replacement in baking recipes. (See tips in this post for which recipes work best with a flax egg.)
Notes
Nutrition information is for 1 flax egg. This information is automatically calculated, and is just an estimate, not a guarantee.
You can use ground chia seeds instead of flax seeds to make a chia egg.
Flax eggs work best in recipes that call for all-purpose or whole-wheat flour and don't require more than 2 eggs. Try them in cookies or brownies where you don't mind a slightly softer, gooey center.
Do NOT use flax eggs as an egg replacement in recipes that call for almond flour or coconut flour. Flax eggs won't provide the structure that chicken eggs do, so they also aren't a great fit for flourless recipes.
See the full post above for more tips on using flax eggs.