Melt the 2 tablespoons butter in a large, heavy skillet.

Add the onions and cook on medium-low heat for at least 30 minutes, stirring occasionally, until they become a golden caramel color.

Transfer the caramelized onions to a container and set aside.

Combine the ½ cup butter, flour, and salt in the bowl of a food processor and process until the butter is mostly incorporated.

Slowly drizzle in enough cold water to make a medium-stiff dough.

Roll the dough out on a floured surface to ⅛-inch thickness.

Cut the dough into 6-inch circles and chill until ready to bake.

Preheat the oven to 350 degrees.

Spread a layer of caramelized onions on the top of each circle of tart dough.

Top with fresh or sun-dried tomatoes, followed by the goat cheese and fresh oregano.

Drizzle with a little olive oil, and sprinkle with sea salt.

Bake the tarts for about 20 minutes, or until the crust is fully cooked but not too dark.

Remove from the oven, let cool for a few minutes, and carefully remove from the baking pan.

Serve warm or at room temperature.