onion tart with mustard and fennel

INGREDIENTS

• 2 1/4 teaspoons active dry yeast (a 1/4-ounce package)
• 1/2 cup warm water (105 to 115°F)
• 1 1/2 to 1 3/4 cups all-purpose flour
• 1 large egg
• 1/3 cup plus 1 tablespoon extra-virgin olive oil, divided
• 2 1/2 teaspoons salt, divided
• 2 teaspoons fennel seeds
• 3 pound yellow onions, halved and thinly sliced
• 1 tablespoon Dijon mustard (I use a bit more)
• 1/2 cup grated Parmigiano-Reggiano (I like it coarsely grated for this)