In a food processor, briefly pulse salt, sugar, flour and butter until crumbly, approx. 5 sec. Add eggs and process, approx. 5 sec; do not over-work dough or it will be tough and brittle. Turn out onto floured surface and knead until smooth, gathering together all bits, approx. 2 min. Shape into disc and chill 2 hr or until ready to use. Dough can be made three days in advance or frozen up to one month and thawed overnight in refrigerator.
Preheat oven to 375 degrees. Pull tart dough from fridge and let rest 15 min. Warm preserves gently in saucepan over med heat with butter, cardamom, vanilla and flour until combined and thickened slightly, approx. 2 min; reserve and keep warm. On floured work surface, roll out tart dough to 1/8” thickness, 16″ rough diameter. Repeatedly flour pin, board and dough. Transfer to parchment-lined baking sheet. Trim any odd edges, though only a rough oval or circle is needed. Place a single-layer of evenly-spaced Brie slices across bottom of tart, leaving 2″ border; Brie will not cover tart completely. Spoon half of preserves mixture over Brie and sprinkle with half of walnuts, leaving a 2-inch border. Place sliced pears in bunches over Brie, covering completely. Top with remaining preserves mixture, spreading evenly over fruit. Fold edges of tart over fruit, pleating every few inches, brushing edges with egg. Bake 40 min or until edges are golden, center of tart is bubbling and fruit is soft. Top with remaining walnuts and more Brie for garnish. Let cool slightly prior to cutting. Serve warm.