Potato Gratin with Fennel & Tomatoes

I love that brief moment every fall when the days are warm and sunny...the nights are downright chilly...and the farmers' market is filled with not only the abundance of the new season (winter squash, sweet potatoes and other root vegetables, apples & pears, greens...) but also the final odds and ends of the summer crop (tomatoes, peppers, eggplant, green beans...).  Some of my favorite foods fit neatly into this moment—foods that utilize the remains of the summer produce in ways that satisfy my natural craving for the warmer, heartier foods of Autumn:  corn chowder made with chunks of sweet potatoes, Moussaka, rich warming stews of eggplant, tomatoes and summer squash or polenta with the last of the sweet corn folded in.  For dinner a few nights ago we had a potato gratin that fits perfectly into this short in-between season. 

I don't remember the original inspiration for this particular gratin.  I made it for the first time over ten years ago.  I suspect that it is a dish that came about as a way to use up the remainder of a large head of fennel (my original notes call for half of a head of fennel).  Since I would have recently returned from Provence around that time, a French-style gratin filled with the very Provençal flavor combination of fennel, tomatoes, garlic and thyme would have been an obvious direction to go.   

This is not a gratin that I think to make every year.  The inclusion of vine-ripened tomatoes makes it a bit unusual.  Often the tomato crop is over by the time I'm in the mood for a potato gratin.  But as I have mentioned in previous posts, this has been an amazing year for tomatoes.  And now, even as the waning of the light has signaled to the tomato plants that it's time to slow down production, the tomatoes are comparatively abundant and I have continued to bring home as many as I think we can manage to consume in a week.  I am still enjoying them sliced and simply dressed with salt, pepper, vinegar and olive oil, but a large portion of them are now making their way into the aforementioned stews and casseroles.  A couple of Jet Stars were just right for this gratin. 

Up until a year or two ago I had always made this particular gratin with all broth.  Then, I ran across a similar recipe that included a bit of cream. This small amount of cream is inspired—adding much more in the way of warmth and richness than one would anticipate from its volume.  You can of course make the gratin with just broth (see the notes at the bottom of the recipe)...and doing so will make a lighter gratin (fitting even for the still hot temperatures of late summer)...but I really prefer it with the cream.

I love everything about this gratin.  It is rich without being heavy, in sync with the season, and filled with flavors reminiscent of one of my favorite places in the world....satisfying in every way.  So, if you happen to have some late season tomatoes sitting on your counter....looking for  a home...you should give this a try.  Or, if you get up this Saturday morning...and it is chilly and dark...and the thought of your bed is more appealing than a cold trip to the farmers' market...  Think of those last tomatoes....and the possibility of this gratin for dinner...and then get up and go.

Potato Gratin with Fennel & Tomatoes

1 T. olive oil, more as needed

1 small (or half of a large) bulb of fennel (weight when trimmed of stalks should be about 6 oz.), halved, cored and sliced very thinly (use a mandolin) crosswise—you should have about 1 cup of sliced fennel

1 small (or half of a medium) onion (4 oz.), thinly sliced

2 cloves garlic, thinly sliced cross-wise

Salt & pepper to taste

2 small or 1 large tomato (1/2 lb.)

1 1/2 lb. russet or Yukon gold potatoes

2 to 3 t. picked thyme, coarsely chopped

1/2 c. Heavy cream

1/2 to 3/4 c. chicken (or vegetable) stock

1/3 c. grated Parmesan (1 oz.)

Warm the olive oil in a medium sauté pan set over medium heat.  Add the fennel, onion and garlic along with a pinch of salt and toss to coat in the oil.  When the vegetables begin to sizzle, reduce the heat to low, cover and cook until just tender—about 15 to 20 minutes.  Set aside.

While the onion and fennel cooks, peel the tomatoes (by blanching and shocking or using the method outlined in this post).  Place a sieve over a bowl, halve the tomatoes crosswise and remove the seeds while holding the tomato halves over the bowl.  Thinly slice the tomatoes halves and reserve separately with their juices. 

To build the gratin, lightly oil a shallow 1 1/2 quart baking dish.  Peel the potatoes and using a mandolin, slice the potatoes crosswise very thinly (1/16-inch).  Shingle half of the potatoes into the gratin in overlapping rows.  Season with salt, pepper and a third of the thyme.  

Spread the fennel-onion mixture over the potatoes in an even layer and season in a similar manner. 

Next, layer in the tomatoes, spreading evenly.  Pour the reserved tomato juices over the tomatoes.  Season with salt, pepper and the remaining thyme.  

Layer in the remaining potatoes and season with salt and pepper.  

Pour the cream over all, jiggling the dish slightly to make sure the cream penetrates all of the layers of vegetables.  Pour in enough chicken stock so that the vegetables in the middle are just barely covered with liquid when pressed with a spatula or your hands. 

Cover the gratin tightly with foil and place on a baking sheet.  Place in the center of a preheated 375° oven and bake until the cream and stock are bubbling around the edges—about 30 to 40 minutes.  Remove the foil, scatter the Parmesan evenly over the gratin and continue to bake until the cream is reduced and bubbling thickly, the top is a beautiful golden brown and the potatoes are tender to the tip of a knife—another 30 to 40 minutes.  Cool briefly before serving.  Serves 4 to 6.

Notes:  To make the gratin without heavy cream simply omit it and add stock to the appropriate level in the dish—you will need 1 to 1 1/4 cups of stock.  Drizzle the gratin liberally with olive oil before covering with foil.  I have never tried it, but I think this all-stock version would be delicious with saffron.  To make, steep a pinch of saffron 3/4 cup of the hot stock before pouring it over the gratin.  Again, add as much more plain stock as is necessary to properly moisten the gratin. 

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