If you'd think you would appreciate sparkling wine and outstanding patisserie, then I highly recommend the Four Seasons in Georgetown.

http://www.fourseasons.com/washington/dining.html

I had this brunch this past spring. The food was very good, but not outstanding (but that's really typical of Sunday brunches, unless you head over to the top hotels in Asia). Service was efficient. They served unlimited Chandon Brut Classic.

The highlight for me as a gourmand was the dessert table. Classic french pastries galore, including macarons just like in Paris.

The price was $65 plus tax and tip.