Pulse flour and salt together in a food processor to mix. Add the butter cubes and pulse until mixture resembles wet sand. Whisk together sour cream and lemon juice, add and pulse. Slowly drizzle in just enough ice water until a soft dough is formed.
Knead dough into a ball and then flatten into a disk. Wrap very well in cling film and refrigerate for at least an hour.
For the mushroom filling:
Heat olive oil in a large frying pan. Fry the onion until golden brown and beginning to caramelize. Add the garlic, thyme and rosemary. Cook until fragrant. Add the mushrooms and cook until golden brown. Season well. Remove mushrooms from the heat and turn out onto a chopping board to cool. Discard herb stems.
Preheat oven to 200˚C.On a lightly floured surface, roll out cold, rested pastry into a large 30cm circle. Transfer onto a baking tray lined with baking paper. Sprinkle a little cheese over the base of the pastry. Toss the remaining cheese with the cooled mushrooms.
Arrange the mushrooms in the center of the pastry leaving a 4cm border. Fold the border up and over the filling, pleating along the way to seal the border. Place cherry tomatoes around the mushroom filling and sprinkle with a little salt.
Egg wash the pastry and season. For extra points sprinkle a little cheese on the pastry edges. Bake in the oven for 45-50 minutes until the pastry is cooked through and deeply golden brown. Allow to cool slightly before cutting into slices and serving.
Upland Brandy Sidecar: (makes 1 cocktail)
In a shaker filled with ice combine the brandy, triple sec and simple syrup. Shake well. Strain into glass over ice and garnish with a twist of orange.