Jarlsberg & Mushroom Tart with Soured Cream

Method

1. Finely chop the onion. In a large skillet, melt a little butter over medium heat and sauté the onion until soft and translucent, without browning. Transfer to a plate.
2. In the same skillet, increase the heat to high and add a little more butter. Add the sliced mushrooms and cook, stirring constantly, until all liquid evaporates and they are quite dry. This may take 8–10 minutes.
3. Return the cooked onion to the skillet with the mushrooms, stir to combine, and season with salt and pepper. Let the mixture cool completely.
4. Roll out the pastry on a lightly floured surface to a thickness of about 3–4 mm. Line a shallow 24 cm springform cake tin with the pastry, pressing it into the bottom and up the sides to a height of about 4–5 cm. Trim any excess. Chill the pastry-lined tin for 30 minutes.
5. Preheat the oven to 400°F / fan 350°F / gas 6. Line the pastry with parchment paper and fill with baking beans or dried pulses. Blind bake for 15 minutes, until the edges are set and the pastry feels firm.
6. Remove the paper and beans, then return the pastry to the oven for another 5–10 minutes to dry out the base. Let it cool slightly.
7. Spread the cooled mushroom-onion mixture evenly over the pastry base. In a small bowl, mix two-thirds of the beaten eggs (about 2 eggs) into the soured cream until smooth. Pour this mixture over the mushrooms.
8. Sprinkle the grated Jarlsberg cheese over the top. Brush the exposed pastry edges with the remaining beaten egg.
9. Bake the tart for about 30 minutes, or until the filling is set and golden brown on top. Let it cool in the tin for 10–15 minutes before removing the ring. Serve warm or at room temperature.