Thank you to those who suggested places near 3rd and 15th. In the end, we went to Verbena as I first thought we might.
This place is worth a visit even just for the beverages! Instead of cocktails, we had 3 sodas (ginger, vanilla, and verbena) and a yuzu lemonade. The sodas -- all house-infused syrups -- were quite sweet but well-flavored. The lemonade was incredibly wonderful: very citrusy/flowery from the yuzu, quite tart but just sweet enough to balance. I could see whiling away many a summer afternoon drinking this.
Three of us had the 3-course, $30 prix fixe; my husband ordered a la carte (although he almost got the 5-course vegetable tasting menu, ?$45?). Our friends had the green salad -- nice, but only nice; I had Wild Mushroom Bisque with tarragon oil. Only a tiny bit of cream, great mushroom flavor, and slices of some sort of very pale green veg in the bottom of the bowl -- looked like scallion but not at all oniony, just crunchy and vegetal. Hubby had sauteed morels with favas. Lots of mushrooms, very well-flavored.
Hubby's spice-laquered duck (sliced breast, braised leg) came with very delicate pea shoots and little round potato croquettes. The 3 of us had chicken, a very moist, flavorful boned flattened breast with CRISP golden skin, over baby bok choy and white beans with rosemary, black olive slivers, and lemon in a chicken jus. One of our friends said it tasted better than any other chicken he had ever eaten.
Wine was a Catalonian "Gine Priorat" that we'd never heard of; only $29, pleasant but not great. Went fine with the food, so it was a bargain.
Dessert on the prix-fixe was either sorbets or verbena creme brulee. The sorbets were rhubarb, pineapple, grapefruit, and mixed berry (some of each). The creme brulee was deconstructed: instead of torched sugar on top, there was a light verbena-flavored syrup poured over a very solid vanilla cream, with a buttery, nutty lace cookie laid across the top. I usually avoid cb like the plague, but I really wished I could have finished mine. Hubby had a savarin cake with bittersweet chocolate ice cream and chocolate sauce. VERY chocolate.
With one coffee and one tisane, the bill was $200 with tax, before tip. Service was good. We never felt any problem because most of us were "eating cheap."