• Fresh basil for garnish
In a bowl of an electric stand mixer on medium speed (or using a pastry cutter), combine flour and butter and mix until mixture resembles small peas. Refrigerate for 10 minutes. Add bacon and mix at low speed until just combined. Add sour cream, 1/4 cup at a time, mixing just until blended after each addition.
On a heavily floured work surface, sprinkle dough lightly with flour and knead 3 to 4 times, adding more flour as needed. Using a floured rolling pin, roll dough into a 13-inch round. Gently transfer dough to a 9-inch fluted tart pan with 2-inch sides and a removable bottom. Press dough into pan; trim off excess dough along edges. Refrigerate 30 minutes.
Meanwhile, cut 2 pounds of tomatoes into 1/4-inch thick slices, and remove seeds. Places tomatoes in a single layer on paper towels and sprinkle with 1 teaspoon salt. Let stand 30 minutes.
Preheat oven to 425 degrees. In a medium bowl, stir together Cheddar cheese, Parmigiano-Reggiano cheese, mayonnaise, egg, dill, chives, parsley, vinegar, green onion, sugar, black pepper and remaining 1 teaspoon salt, mixing until combined.