Prepare the dough. In a small bowl, mix the warm water, sugar, and yeast. Let it sit for 5–10 minutes until foamy. In a large bowl, combine the flour and salt. Add the yeast mixture and olive oil. Knead for about 10 minutes until smooth. Cover and let rise in a warm place for 1 hour.
Cook the onions. Heat olive oil in a pan over low heat. Add onions, garlic, thyme, and black pepper. Cook slowly for 30–40 minutes, stirring occasionally, until soft and caramelized. Let cool.
Assemble the pissaladière. Preheat oven to 220° C (425° F). Roll out the dough into a thin rectangle or circle and place it on a baking sheet. Spread the caramelized onions evenly over the dough. Arrange the anchovies in a crisscross pattern, placing an olive in each diamond shape.
Bake. Bake for 15–20 minutes until the crust is golden brown. Let cool slightly before slicing.
Serving Suggestion. Serve warm or at room temperature with a side salad and a glass of rosé wine.
