I'm hosting an event on Tu B'av and I need to decide on the menu. Are there any foods that are particularly appropriate for the holiday?
I can find no foods that are particularly appropriate for the holiday. In all the descriptions of the day, see for example here there is no mention of special foods (remarkably for a Jewish festival).
Tu B'Av certainly has links to marriage and matchmaking which explains the reference to wedding cake above.
The nights begin to get longer from Tu B'Av which leads to an increase in Torah learning at night which is a special time for learning. This contributes to the happiness for which Tu B'Av is known. So maybe the idea would be to eat foods made from flour based on the mishnah in Avos 3(17) אם אין קמח, אין תורה.
According to my research, Jews of Lebanon and Syria do eat some traditional foods at this time of the year. This includes the following: 1. Harissee : Whole grains of wheat and lamb hamin cooked with Merrill bones, chickpeas, cinnamon sticks cardamom pods, and broth. 2. Marqooq bread or laffa : paper thin bread to serve with hamin 3. Tamriyeh: a dessert made with a pareve water cooked semolina cooked in sugar syrup flavored with orange blossom and mastic grains, then the semolina is cut into cubes covered in an envelope of dough , then fried. These are then sprinkled with powdered sugar. 4. An assortment of fresh grapes 5. A variety of different new wines
...להבין ענין היום טוב של ט"ו באב לעשות בו סעודה של משתה ושמחה
To understand the concept of this Yom Tov of the 15th of Av, to make a festive meal of celebration and happiness...
Later in the essay, after exploring some of the roots and ideas behind the day, he adds:
וממילא יש סמך גם כן למשתה ושמחה ביום זה שנקרא יום שמחת לבו, כי אין שמחה אלא ביין כמו שנאמר "ויין ישמח לבב אנוש"
Therefore, there is what on which to rely for a festive meal on this day which is referred to as "day of his joyous heart" for there is no happiness without wine, as it says "and wine rejoices the heart of man".