Preheat oven to 325° (300° if using convection heat). Crush cookies into fine crumbs either in a food processor or by placing them in a 1-quart zip-lock plastic bag and pounding them with a rolling pin. Pour 2 cups of the crumbs into a bowl and mix with melted butter. Press mixture evenly into bottom and up sides of a 10-inch tart pan. Set aside.

Beat mascarpone, honey, and vanilla at medium speed until smooth. Add eggs one at a time, beating well after each addition. Beat in flour and salt.

Place tart pan in a larger rimmed baking pan and set on center rack of preheated oven. Pour filling into crust. Bake until filling is pale golden and barely set in the center when you gently shake pan, 30-45 minutes for a metal tart pan or up to an hour for glass.

Meanwhile, combine rhubarb and sugar in a small saucepan and bring to a simmer them over low heat. Cover and cook until the rhubarb is soft. Let cool.

Remove tart from oven and let cool on a rack about 30 minutes, then chill until cold, at least 1 hour, or up to 1 day (cover tart once cold).

Before serving, pour rhubarb sauce over tart.