It's one of 100 royally-approved recipes that made the cut of her son Tom Parker Bowles' new book, 'Cooking and the Crown'

Long before Queen Camilla was a member of the royal family, she was mom to children Tom Parker Bowles and Laura Lopes.

Parker Bowles, 49 -- a food writer and the son of Queen Camilla, as well as both the stepson and godson of King Charles -- is combining two subjects he knows well, food and the royal family, in a new cookbook. Parker Bowles' ninth book in 20 years , Cooking and the Crown: Royal Recipes from Queen Victoria to King Charles III, hit shelves Oct. 22, and within its pages are 100 royally-approved recipes, including Queen Camilla's chicken soup (below) -- the ultimate comfort food and what her son calls her "lunchtime staple." (The King, for his part, has been known to historically not eat lunch.)

"I hope it gives readers a taste of British royal family life over the last 180 years," Parker Bowles tells PEOPLE in this week's issue. "Food is a prism through which you can see many things -- history, society and economics."

Though she may be royalty -- the King, 75, and the Queen, 77, are currently on a royal tour of both Australia and Samoa -- not much has changed since the two took the throne, Parker Bowles says.

"I still see my mother and stepfather the same way," he tells PEOPLE, adding that his mother is always accessible: "She'll say, 'Are you around for dinner? Where should we go?' She'll slip into a restaurant, and no one really blinks," Parker Bowles adds.

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"I'm incredibly proud of her," he says. "She's at an age when most people think of retiring, but she never complains; she just gets on with it."

Related: Inside Queen Camilla and King Charles' Diets, According to Her Cookbook Author Son Tom Parker Bowles

2 cooked boneless, skinless chicken thighs, shredded (about 1 cup)

4 cups thinly sliced Savoy cabbage (from 1 small [2 lb.] head)

Chopped vegetables of your choice, like tomatoes and/or scallions

Grated Parmesan cheese, for serving

1. Bring stock to a boil in a large saucepan over high heat. Boil, uncovered, until reduced to 4 cups, about 20 minutes, adding potato in the last 5 minutes. Stir in chicken, carrot and celery; simmer over medium low, stirring occasionally, until vegetables are just tender, about 8 minutes. Stir in cabbage; continue cooking until wilted, about 1 minute more.

2. Remove from heat; stir in lemon juice, salt, pepper and hot sauce (if using). Divide soup among bowls; sprinkle with Parmesan, and serve immediately.

Serves: 4

Active time: 20 minutes

Total time: 40 minutes

From Cooking & the Crown: Royal Recipes From Queen Victoria to King Charles III by Tom Parker Bowles. Copyright © 2024. Reprinted by permission of Ten Speed Press, an imprint of Penguin Random House LLC.