To make the crust, mix butter, sugar, salt, pine nuts, and vanilla in a medium bowl. Add flour and stir until just blended. Press the dough evenly over the bottom and up the sides of a 9½-inch tart pan with a removable bottom. Generously prick the bottom and sides with the tines of a fork. Bake in the lower third of an oven preheated to 350° F until the crust is pale golden, about 20 to 25 minutes. Cool completely.
To roast blueberries, toss berries with lemon juice, honey, salt, and rosemary on a rimmed baking sheet lined with foil. Roast in oven preheated to 400° F until very tender and just starting to collapse, 10 to 15 minutes. Remove from oven. Discard rosemary sprigs (it's okay if a few leaves remain with the blueberries). Set aside to cool to room temperature.
For the cream filling, whisk together mascarpone, honey, cream, and a pinch of salt in the bowl of a stand mixer until smooth and thick, taking care not over-beat. Scrape mixture into the cooled tart crust, spreading it evenly to the edges.
Strain the blueberries over a small bowl. In a separate bowl, toss blueberries gently with reserved lemon zest and a pinch of salt.
Top cream-filled tart crust with blueberries and drizzle with additional honey. Garnish with fresh rosemary sprigs, if desired, and serve with remaining juices.