In a medium heavy-bottom saucepan, melt butter over medium heat. Add squash; season with salt and pepper. Cook, stirring often, until edges soften, 6 to 8 minutes.
Add rice; stir to coat. Add wine; cook until almost all liquid has evaporated, 1 to 2 minutes.
Reduce heat to medium-low; add 1/2 cup hot broth mixture. Cook, stirring, until almost all liquid is absorbed. Add remaining broth mixture, 1/2 cup at a time, stirring until liquid is absorbed before adding more, 35 to 40 minutes total.
Stir in Parmesan, sage, and 1 1/2 teaspoons salt. Serve immediately, garnished with more Parmesan and sage, if desired.