Melt one tablespoon of butter in a skillet over medium to low heat. Add sliced onions, rosemary leaves, and one teaspoon of brown sugar. Cook, occasionally tossing, until onions are limp and golden brown, 10 to 15 minutes. Stir in the balsamic vinegar, and remove from heat.
In a small bowl, whisk together the milk and egg until smooth. Stir in the onions.
Preheat oven to 375°F
Brush the tart pan with melted butter.
Cut the phyllo sheets to a square size to fit your tart pan.
Brush the phyllo sheets with melted butter, then stack them up. Add the phyllo stack to the pan, pressing it into the base. There will be a phyllo overhang; you will take care of that later.
Add the crumbled gorgonzola cheese and pour in the egg mixture and onions.
Arrange figs slices next to each other on top. It's okay to overlap a little.Cut the excess pastry with scissors to about ⅓ of an inch around the tart pan.
Bake until the phyllo pastry is golden and the egg mixture is bubbly for 25 to 30 minutes. If it looks like it has too much liquid on top, it's okay; it will be set after you take it out of the oven. Serve with rosemary leaves, a drizzle of honey, and walnuts. The tart can be enjoyed warm or at room temperature.
Notes
Nutritional Info – Please remember the nutritional information provided is only an estimate and can vary based on the products used.