Lauren Castillo, author of Caldecott Honor book Nana in the City and illustrator of numerous picture books, tells the story of a hesitant child, a single parent, and a calm rescue dog who provides a grounding presence in Just Like Millie (Candlewick, Apr.). Castillo spoke with PW about drawing her Harrisburg, Pa., neighborhood, concise picture book manuscripts, and dogs as icebreakers for the socially anxious.

How did this story of a quiet child and her rescue dog evolve?

It began when I witnessed my friend’s child, who’s very shy, interacting with a dog and watching his demeanor change and his face light up. He seemed more confident and willing to have a conversation with me. Then, I began thinking about my own two dogs at the time. When I would take them out, I was more apt to talk to strangers or neighbors. I thought about the way animals bring connection, and kids who warm up in the presence of their pets or someone else’s.

Is Millie based on a dog you know?

Yes: our dog Peanut. We had two older pups. Peanut has passed away, and I wouldn’t say his personality is like Millie’s, but visually I wanted to honor him by making him the main character. His friend in the park, the little black dog, is our dog Keiko, so they got to be memorialized in the book.

How did you work with your editor on this project?

I’ve illustrated picture books for Candlewick, but this is my first time writing and illustrating for them. Sarah Ketchersid was my editor on a project called Happy Like Soccer, so I was excited to share this story with her. I sent in a full draft, and she helped me pare it down. I was starting to get attached to different lines and whatnot because I’ve been working on chapter books—the Our Friend Hedgehog series—and I got used to being wordy! Before, I was very poetic, and I had to make this mental switch to come back to picture books again, to let the girl’s emotion show in her body language.

How do you create such evocative, recognizable settings?

I really like to draw the environment around me. One of my favorite things to draw is architecture, on location. When I’m drawing things on location, in a quick way, I’m able to capture the energy much better than if I’m making it up or sitting down at the desk. If I’m drawing from photographs, it ends up being more like an architectural rendering.

How much did you draw from your own home city?

Harrisburg is a fairly new city to me. I’ve been here about six years, and I knew I wanted to place [Millie] in my town. I could go out to my favorite spots or take reference photos and bring those back to my studio to build Millie’s world. I got to throw in a lot of Easter eggs, like familiar faces in the neighborhood, landmarks, other dogs. A friend’s mural is in one of the images. Things like that made the process so enjoyable.

I thought about the way animals bring connection.

Can you describe your artistic technique and how you combine hand-drawn and digital art?

I still mostly draw everything by hand. I used a quill pen to draw Just Like Millie so my line would be a little wonky or rough around the edges. That wobbly line brought more energy to the piece. What’s nice about something like Procreate or Photoshop is that I can do, say, 10 drawings of cars, scan those in, and decide which one’s going to fit best. It’s almost like digital collaging my drawings, but they’re all hand-done. I also like to do the final painting by hand: I’ll actually print out the line drawing on watercolor paper, and for Millie I used watercolor and soft pastels [to finish]. The computer’s more of an assist for me in that way.

What else are you working on?

It’s been 10 years since Nana in the City came out, and I have a follow-up called Nana in the Country [Clarion, Feb.]. Nana goes to visit her grandson, who lives in the country, and I drew a lot from the Lancaster area. Since I moved from New York City, where I made that first book, to Pennsylvania where I’m surrounded by rural areas, it felt fitting to do this one so many years later.