Heat oil in a large skillet over medium heat. Add the onion, garlic, and a pinch of salt. Saute for 20 minutes or until the onion is soft and golden brown.
Stir in the white beans, pesto, and sun-dried tomatoes. Cook until heated through and the flavors are married.
Preheat the oven to 400 Fahrenheit. Oil a baking sheet or line it with Silpat and set aside.
Carefully unfold the sheet of pastry onto the baking sheet. With a knife, gently score a line 1/2-inch from the edge of the crust all the way around, making sure not to cut all the way through the dough. Using a fork, generously but gently prick inside the scored line.
Bake the shell for 15 to 20 minutes until golden brown and very puffed. Remove the crust from oven.
Use the back of a spoon to gently crush down the puffed area inside the scored lines leaving a raised 1/2-inch rim all the way around.
Spoon the bean mixture over crust, spreading to the inside edge of rim. Slide onto a cutting board and cut into 8 squares.
Transfer to individual plates or serve right from the cutting board. Garnish as desired.
Note: If not using the crust immediately, remove from oven to a wire rack to cool, then, when ready to use, preheat the oven to 350 Fahrenheit.
Crush down puffed area and fill as described above. Before cutting, place tart in.
Spinach Pesto
Place one-third of the spinach in a food processor. Process until finely chopped. Continue adding the remaining spinach, scraping down sides as necessary. Add the garlic, walnuts, nutritional yeast, if using, lemon juice, and salt, and process to combine. With the machine running, stream in the oil until well incorporated. Do not over-process.

1 tablespoon olive oil
1 medium yellow onion, halved, and cut into 1/4-inch slivers
1 to 2 large cloves garlic, peeled and coarsely chopped
sea salt
1 sheet Pepperidge Farm Puff Pastry, thawed
1 (15.5-ounce) can white beans, rinsed and drained
1/4 cup plus 2 tablespoons spinach pesto (recipe follows)
6 oil-packed sun-dried tomatoes, drained and coarsely chopped
Garnish: red bell pepper strips and rosemary sprigs

Spinach Pesto (yield 1 1/2 cup)
10 ounce fresh baby spinach, rinsed and dried
1 cup lightly packed fresh basil leaves, rinsed and dried
4 garlic cloves
1 cup lightly toasted walnut pieces
1 teaspoon nutritional yeast, optional
1/4 cup fresh lemon juice
1/2 teaspoon sea salt
1/3 cup olive oil