I'm going to keep this short and sweet. The best bottomless mimosa in San Mateo can be found at Osteria Coppa.
Available 'bottomless' on Sundays, not only are the mimosas absolutely stunning, but the Mushroom Frittata (Maitake & Hedgehog Mushrooms, Broccoli Romesco, Goat Cheese Cream) is phenomenal. Beyond that, the staff is on top of it and never allows you to see the bottom of your mimosa. Osteria Coppa is quickly becoming more than a trend for me, but rather a tradition.