Yes, you can substitute unsweetened chocolate for bittersweet chocolate or 70% cacao chocolate by adding sugar to achieve the desired level of sweetness. To do this, you'll need to determine the amount of sugar needed based on the recipe and the quantity of unsweetened chocolate called for.
Here's a general guideline for making the substitution:
Determine the amount of bittersweet or 70% cacao chocolate required in the recipe.
Take the same weight of unsweetened chocolate and add sugar to it. The amount of sugar to add depends on the level of sweetness you desire and the intensity of the chocolate flavor you're aiming for. Typically, 1 ounce (28 grams) of unsweetened chocolate can be combined with around 1 to 2 tablespoons of sugar.
You can start by adding 1 tablespoon of granulated sugar to 1 ounce of unsweetened chocolate, mix it well, and taste the mixture. If you find it's not sweet enough, you can add more sugar gradually, adjusting to your taste preferences.
Remember to melt the unsweetened chocolate and sugar together, incorporating them into your recipe according to the instructions. Keep in mind that the texture and consistency of the final product may differ slightly from the original recipe due to the differences between unsweetened and bittersweet chocolate.
It's important to note that the substitution will affect the overall flavor and sweetness of the recipe, so it's recommended to perform a small test batch or consider experimenting with the proportions to achieve the desired results before making the full recipe.