Summer has turned to fall as fast as the click of an on-off switch.

That means retiring the A/C, and turning on the oven instead without guilt to warm things up.

“Cornish Game Hen Dijonnaise” is a worthy dish to mark that transition.

A succulent dish that roasts in the oven and creates its own lusty sauce in the process, this recipe is from “Feasts on the Farm” (Chronicle Books), of which I received a review copy.

It was written by Tamara Jo Hicks, owner of Toluma Farms in west Marin County, and Jessica Lynn MacLeod, a longtime volunteer there who developed the recipes.

Hicks and her husband bought the 160-acre farm in 2003, restoring the land to raise goats and sheep. In 2013, they began making their own farmstead cheeses under the label of Tomales Farmstead Creamery.

The book celebrates the agrarian beauty of Northern California, and its agricultural history. At its peak, there were more than 300 dairies in Marin County. Now, Hicks and MacLeod write, there are fewer than 30.

With more than 60 recipes arranged by the seasons, the book makes you appreciate all the more that farms and dairies like these still exist to provide delicious artisanal products that enrich our lives and diets.

Tuck into everything from “Crisp Popovers with Goat Kefir and Mulberry Rhubarb Compote,” “Balsamic Salad Pizza,” and “Lamb and Pork Sausage Cassoulet” to “Gravensteiin Apple and Marmalade Grilled Cheese” and “Campari Hazelnut Cake.”

This Cornish game hen dish gets flavored with fennel, lemon, and rosemary, as well as a generous amount of Dijon mustard.

I took the opportunity to up the mustard game by using some Apple Valley Country Store Dill Mustard that I had picked up at its cute little store in Hood River, OR earlier this year. This family-owned store has been making jams, jellies, mustards, and pies for almost 30 years.

The dill mustard amplifies the grassy, anise taste of the fresh fennel in the recipe. But regular Dijon mustard will be plenty flavorful in this recipe, too. The Apple Valley Country Store is is currently sold out of the dill mustard, but let’s hope it restocks because it’s delicious on sausages and pork chops, too.

Chop up some fennel, then place in a baking dish or cast-iron skillet. Stuff the cavities of two Cornish hens with rosemary and lemon halves, then place atop the fennel. Brush the hens with mustard mixed with olive oil, then roast in the oven until done.

Carefully turn the hens vertically atop the pan so that any juices fun out onto the fennel. Remove the birds to a plate, and tent with foil to keep warm.

Transfer the fennel and juices to a saucepan, Add more Dijon, plus butter and olive oil, and simmer until thickened.

Place half a hen on each of four plates, spoon over the sauce, and garnish with some fennel fronds.

The birds boast crispy, bronzed skin and moist, succulent flesh. The mustard turns the sauce so creamy while adding a delicious sharpness that’s softened just so by the anise note.

I love dishes like this that require only a handful of ingredients, where the oven does the majority of the work, and the resulting pan sauce really has oomph. No doubt, you will, too.

Cornish Game Hen Dijonnaise

(Makes 4 servings)

1 fennel bulb (about 1/2 pound), roughly chopped

1/4 cup chopped fennel fronds, reserved for garnish

2 Cornish game hens, patted dry and at room temperature

1 lemon, halved

4 fresh rosemary sprigs

5 tablespoons Dijon mustard

3 tablespoons extra-virgin olive oil

2 teaspoons kosher salt

1 tablespoon unsalted butter

1 tablespoon freshly ground black pepper

Preheat the oven to 400°F (200°).

In a 6-by-8-inch baking dish or 9-inch cast-iron skillet, spread the chopped fennel in a single layer. Place the hens on top of the fennel with some space between them so they aren’t crowded.

Stuff the cavity of each hen with half a lemon and 2 sprigs of rosemary. Mix 2 tablespoons of the olive oil and brush the top of each hen evenly. Sprinkle the salt evenly over each hen and truss the legs with cotton string.

Bake for 45 minutes, turning halfway through to ensure even browning. When removed from the oven, insert a knife into the space between the thigh and body. If the juices run clear, the hen is done. Turn the hens vertically when removing them from the pan to release any additional juices before placing them on a carving board. Tent with aluminum foil to keep warm.

Transfer the juices, fennel, and any remaining contents from the baking dish into a large saucepan. Add the remaining 3 tablespoons of Dijon to the saucepan along with the remaining olive oil, the butter, and pepper. Simmer gently over medium heat for 5 to 7 minutes until slightly reduced and thickened.

To serve, carve the hens and arrange on a serving platter or plate individually. Spoon the sauce and fennel over the hens and garnish with fennel fronds to serve. The hens and sauce can be stored in an airtight container in the refrigerator for up to 5 days.

From “Feasts on the Farm” by Tamara Jo Hicks and Jessica Lynn MacLeod

More Cornish Hen Recipes to Enjoy: Thai Cornish Game Hens with Chili Dipping Sauce

And: Cornish Game Hen Soup with Fried-Shallot Oil