Mix dough. Whisk together 2 cups warm water and package of yeast in the bowl of a stand mixer. Let sit 5-10 minutes until creamy and beginning to foam.
Add 2 cups of the flour, 3 tablespoons of the olive oil and 2 teaspoons of the salt. Chop the fennel seeds with a sharp knife or crush them using a mortar and pestle. Measure out 1/2 teaspoon of the fennel and add that to the flour mixture along with the black pepper.
Using the dough hook attachment, begin mixing on low. Once the ingredients are well combined, add remaining flour, about 1/2 cup at a time, until a soft, sticky dough is formed (you may not use all the flour). The dough should not cling to the sides of the bowl but will still be soft and sticky at the bottom of the bowl. It is better for the dough to be too wet, then too dry. Increase the speed to medium and knead the dough for 8 minutes.
First rise. Oil a large bowl and transfer dough to oiled bowl. Turn the dough so it is covered in oil. Cover tightly with plastic wrap. Let rise in a warm place until doubled in size, about an hour.
Press into baking sheet. Line a small baking sheet with parchment paper, (the smaller your baking sheet the thicker the focaccia will be). Oil the parchment paper well. Using oiled hands, slide dough onto baking sheet preserving as many air pockets as possible. Gently pull and stretch dough to the edges of baking sheet (oil hands again if they get sticky).
Spray one side of plastic wrap with baking spray. Cover pan loosely with the plastic wrap, oiled side down and let rise in a warm, draft-free area until slightly puffed, about 30 minutes.
Heat oven to 450°F and arrange rack in the middle. Press fingertips all over dough to form indentations. Drizzle top of dough with remaining 2 tablespoons of olive oil and sprinkle with remaining 1/2 teaspoon crushed fennel, 1 teaspoon salt and 1 tablespoon chopped rosemary. Let bread continue to rise while you wait for the oven to come to temperature.
Bake focaccia until firm to the touch and lightly browned, about 20 minutes.
Cool and serve. Remove focaccia from the baking sheet, transfer to a rack and drizzle with another tablespoon or so of olive oil if you'd like. Cool at least 10 minutes before slicing and serving.