Whirl 1 cup flour, the masa harina, and salt in a food processor to blend. Add butter and pulse until crumbly. Add cream cheese in small pieces and whirl until dough comes together. Shape dough into a 3-in.-thick log. Cut in half crosswise to make 2 disks, wrap each in plastic wrap, and chill at least 1 hour and up to 3 days.
Preheat oven to 400°. Toss vegetables in a large bowl with chopped thyme and oregano, garlic, 3/4 tsp. salt, the pepper, and 1/4 cup oil. Spread vegetables in a single layer on a rimmed baking pan.
Line another rimmed baking pan with parchment and place tomatoes, cut side down, on sheet. Brush with remaining 1 tbsp. oil, sprinkle with salt, and scatter with sage and thyme sprigs.
Roast vegetables and tomatoes until vegetables are light golden and very tender and tomato skins are browned and very tender, 30 to 40 minutes. Halfway through cooking, rotate trays and turn vegetables (except tomatoes) with a spatula.
Meanwhile, halve each dough disk horizontally. On a lightly floured board, roll each into a 7-in. round. Lay rounds on 2 baking pans lined with parchment; chill until ready to bake. Whisk together egg and 2 tbsp. water in a small bowl.
Roughly chop tomatoes when cool enough to handle. In a large bowl, gently toss chopped tomatoes with roasted vegetables, olives, basil, 1/2 cup fontina, and 3 tbsp. parmesan. Reduce oven temperature to 375°.
Roll edge of each dough round over on itself to form a thick rim. Mound about 3/4 cup vegetable mixture in center of each; spread even. Sprinkle with remaining fontina and parmesan.
Brush exposed crusts with egg wash. Bake tartlets until golden, about 35 minutes, switching pans halfway through. Serve warm, scattered with oregano sprigs.
*Find masa harina in well-stocked grocery stores and Mexican markets.