Caramelized onion and Gruyere puff pastry roll (French onion soup style)

Heat a little olive oil, add the sliced onions and toss to coat; caramelize slowly without burning, letting them darken.

Add butter and about a quarter teaspoon of thyme; continue cooking.

Add a few tablespoons of beef broth, let it soak in, then a little more.

Add a third of a cup of vermouth or white wine and let it bubble away.

When almost all the liquid has evaporated, stir in a tablespoon of flour so the filling is not loose; cook a moment, then take off the heat to cool.

On a floured sheet of puff pastry, spread the onions evenly and cover with Gruyere.

Roll up lengthwise using the paper to help, and seal the edge.

Trim the empty ends, move the log onto a parchment-lined baking sheet, snip along it with scissors and push the cuts alternately to each side.

Brush all over with the egg yolk beaten with a tablespoon of water.

Bake at 425F about 25 minutes until golden brown.

Cut and serve.