Wolfgang Amadeus Mozart  and his sister Maria-Anna, called 'Nannerl'

Wolfgang Amadeus Mozart  and his sister Maria-Anna, called 'Nannerl' by  Eusebius Johann Alphen, on ivory. Mozart Museum, Salzburg, Austria German, out of copyright.

The program for the current season at Tanglewood seems to have been deliberately curated to present beloved, familiar works by Beethoven, Brahms, Mozart, Mendelssohn and others, interspersed with works that are unfamiliar to the audience — both new works by contemporary young composers and rarely-played works by classical composers.

This weekend gives us an opportunity to hear an interesting mixture of three well-known masterpieces together with two unfamiliar works by known composers. One of these unfamiliar works is by Mozart! (And here you thought you knew all of Mozart’s works ...)

The unfamiliar Mozart composition is the Piano Concerto in E-flat, K. 365. This is not an ordinary piano concerto. It is a concerto for orchestra and two pianos, probably written when Mozart was 23 years old and especially designed for him to play with his sister.

Maria Anna Mozart, whom the family nicknamed “Nannerl,” was five years older than Mozart and a gifted keyboard player. She was never expected to become a professional musician, a path not socially acceptable for girls in 18th- and 19th-century Europe. She and Wolfgang were exceptionally close: they had a private language, enjoyed constant play, and Mozart wrote some of his pieces especially for her after they had both grown to adulthood.

This concerto is written for a small orchestra, and unlike in many of his solo piano concertos, Mozart does not give this group (strings and a few woodwinds) much to do other than offer discreet accompaniment. Rather, Mozart seems to concentrate on the two pianos, delighting in the potential for the constant exchange of musical material and the possibilities of intimate dialogue. Neither soloist appears to dominate; rather they are equal partners in the flow of the work.

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The first movement is broad and rich in invention. In the slow movement, especially, the orchestra seems to sit back and watch the two soloists enjoy each other’s company. The last movement is lively and full of fun.

The other unfamiliar work is by another famous composer’s sister: Fanny Hensel (née Mendelssohn). She was four years older than Felix and endowed with great musical talent. Just like the Mozart siblings, Fanny and Felix were extremely close. They doted on each other, even after Fanny’s marriage (to Wilhelm Hensel, an artist), constantly exchanging letters and musical ideas. (Felix always accepted Fanny’s musical suggestions when he sent her drafts for her comment. He called her “Minerva,” after the Roman goddess of Wisdom.) So when Fanny died of a stroke at the tragic age of only 42, Felix was inconsolable. His profoundly moving Sixth String Quartet in F minor is dedicated to her memory. Its subtitle is “Requiem for Fanny.” Only six months later, he, too, was felled by a stroke. He was only 38.

Fanny was an accomplished pianist and a prolific composer, producing many solo piano pieces, chamber music, songs and cantatas. However, her potential career as a professional musician was also curtailed by prevailing cultural and societal norms. She very rarely played the piano in public, and most of her works were not published during her lifetime. It was considered perfectly natural that she should restrict her musical endeavors to the weekly family concerts, and even Felix, fully cognizant of the nature of German society at the time, agreed with this decision. As a tribute to her talent, he even published some of her music under his name. After she died, he worked to collect and publish her works under her own name. In recent years scholars and publishers have brought most of her compositions into the light.

The C-Major Overture is Fanny’s only work for orchestra alone. It was written in the early 1830s, which would mean that its composer was in her mid-20s at the time. It is both tuneful and forceful by turns, with a remarkable intensification of tempo throughout its approximately 10 minutes of performance. It starts with a slow introduction and moves into an “allegro di molto” (“very fast”) before plunging out into the main body of the work (“con fuoco”—"fiery”). The final section of the overture is marked “piu presto e sempre accelerando” (“even faster and continually accelerating”). This compelling work should encourage us all to seek out more of her compositions.

With Prokofiev’s “Classical” Symphony and Brahms’s First Piano Concerto on the program for Saturday evening and Felix Mendelssohn’s own Symphony No. 5 on Sunday afternoon, the other works on the Tanglewood schedule this weekend offer nothing but beloved masterpieces of the first order.

Jeremy Yudkin is professor of music and director of the Center for Beethoven Research at Boston University. He gives preconcert talks for Tanglewood weekends every Saturday at 2:30 p.m. at the Lenox Library.