Robbie Jordan makes these easy muffins as a breakfast special. She finds baking while the restaurant is closed, or prepping for the day before, is a good time to think about the mystery at hand. Here's a clip from the book as she starts to make the muffins:
I headed into the restaurant. Busying my hands with cooking often allowed new ideas to bubble up into my consciousness. When my cat perked up and trotted after me, I said. “Yes, Birdy, you can come, too.” I hauled butter, eggs, and milk out from the walk-in, grabbed a couple of big bags of mini chocolate chips, and fired up the wide oven. I mixed the dry ingredients—flour, baking powder, salt, and sugar—then broke the eggs into a well in the middle and used a fork to stir them in, thinking as I worked.
Preheat oven to 375 degrees Fahrenheit. Grease a standard muffin tin or line with cupcake papers.
Combine the dry ingredients in a mixing bowl.
Make a well and break the eggs into it.
Stir them with a fork to slightly mix. Add oil, milk, vanilla, and chocolate chips, and mix in with a fork until barely combined.