Approximately five years ago, my good friend from college and I road-tripped from Maine to the Jersey shore to spend the summer working at a local coffee shop in Ocean City, New Jersey.  Laura and I stayed with my friend Craig along the way, and he surprised us in the morning with an incredible frittata made with caramelized onions.  Craig was both a chemistry major and amazing cook, and on that morning, I learned that you could add water while caramelizing onions and turn up the heat a bit so that it wasn’t an hour long process to get those onions nice and sweet.  Game changer!

The Chemistry of Caramelizing Onions

Caramelization is the oxidation of sugar that results in a brown color and tasty nutty flavor.  When you apply heat to onions, and the onions reach a certain temperature (at least 212 degrees F), the complex sugar molecules/ starch (poly and disaccharides) that are present in onions are broken down into monosaccharides (single sugar molecules).  This process is known as pyrolysis, and results in the darker color and sweeter taste.  I like to add salt to speed up the process and a little bit of wine when the onions stick to the bottom of the pan.

Caramelized Onions, Spinach,Goat Cheese & Sun-Dried Tomato Quiche

 Pie Crust Ingredients:

• 1 1/3 cups flour
• pinch salt (approximately 1/2 tsp)
• 1 stick (1/2 cup) cold butter
• 1/3 cup ice water (as needed)

Quiche filling ingredients:

• 1 tbs olive oil (you can also substitute butter)
• 1 large finely diced sweet yellow onion
• 1 tsp salt
• 1/4 cup white wine
• 6 oz spinach (I used 1 bag of spinach from Trader Joe’s)
• 4 large eggs
• 1/2 cup whole or 2% milk
• 1/3 cup soft goat cheese
• 1/4 cup chopped sun dried tomatoes
• Freshly ground pepper
• Fresh basil (for garnish)

Pie Crust

Preheat oven to 400 degrees F.

Mix flour and salt to blend. Cut cold butter into flour using either a food processor (on very low speed) or 2 knives.  Try not to overwork the dough.  It should be course with small (smaller than pea sized) approximately evenly sized clumps of butter. Drizzle a tiny bit of the ice water onto the dough and turn out onto a lightly floured work surface. Press dough into a ball and refrigerate for 30 minutes while you caramelize the onions.

Caramelize the Onions

Heat oil in a large skillet over medium heat.  Add onions and salt, and reduce heat to medium/low.  Cook, stirring every few minutes, and adding a dash of wine whenever the onions begin to stick to the bottom of the pan. Cook for approximately 30 minutes or until onions are a soft, caramel color.  Add spinach to the caramelized onions and mix over medium heat until spinach wilts slightly.

Roll out the Pie Crust

Remove crust from the fridge and turn out onto a lightly floured surface.  Using a rolling pin, roll the dough into a large circle so that it is slightly larger than your tart pan.  Note, I often roll out the dough in between two sheets of parchment paper to avoid sticking.  Place dough in quiche pan pressing down to line bottom and sides with dough.  Fill in any missing pieces with extra dough.

Partially blind bake the dough  for approximately 20 minutes at 400 deg F.  Cool to room temperature while you finish preparing the filling.

Reduce oven temperature to 350 degrees F.

Continue the Filling

Chop goat cheese into small chunks and slice sun-dried tomatoes into strips.

In a large  bowl, using a whisk, beat eggs and milk until light and frothy.  Stir in goat cheese and sun-dried tomatoes so that chunks of cheese and tomatoes are evenly distributed in egg mixture.

Assemble the Quiche

Spread spinach and caramelized onions evenly over partially baked crust.  Slowly pour the egg mixture into the crust mixture making sure to distribute ingredients evenly.

Bake in the middle of the oven for approximately 40 minutes or until a knife or toothpick inserted into the middle comes out clean.  Let cool on a wire rack.

Top with a sprig of fresh basil and enjoy!

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For more information on caramelization check out the following Blog Posts and Articles:

1. Kinetics of non-enzymatic browning in onion slices during isothermal heating

2. Caramelizing Onions by Meme Inge
3. Science of Cooking