Final answer:
The word that best completes the phrase is 'stove' since it is a tool used for cooking, similar to how a paintbrush is a tool used for painting.
Step-by-step explanation:
The word that is the best fit to complete the phrase '_ is to cooking as a paintbrush is to painting' is stove. A stove is a crucial tool in cooking, just as a paintbrush is essential for painting.
While a recipe is more like a blueprint or plan and an ingredient is a component of the dish, much like paint to a painting, the stove and the paintbrush are the instruments through which the creation process happens. A chef is more akin to the artist themselves rather than the tool used in the process.
Therefore, the stove equates to the paintbrush in the context of being a tool necessary for the execution of their respective tasks.