1. Pulse flour, salt, sugar in food processor.
2. Add butter, pulse until pea-sized.
3. Add starter and egg, pulse until dough starts coming together.
4. At this point, if dough is still crumbly, turn out onto the counter. Slowly add ice water until dough comes together.
5. Form into round disc, wrap, refrigerate for at least 30 min and up to several days.