Importing the class

Link to importing-the-class

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

import mods.createtweaker.MixingRecipe;

Extending BasinRecipe

Link to extending-basinrecipe

MixingRecipe extends BasinRecipe. That means all methods available in BasinRecipe are also available in MixingRecipe