Mustard Pastry Tomato Tart with Caramelized Shallots
A sophisticated open tart combining buttery, mustard-spiked pastry with slow-cooked shallots and thin-sliced tomatoes that caramelize in the oven. The crust is made with both butter and lard for tenderness and flavor, while Dijon mustard brushed on the base adds a subtle tang that complements the sweet shallots and bright tomatoes. Thyme runs through both pastry and filling, unifying the flavors. This is an elegant yet approachable dish for home cooks seeking something beyond standard savory tarts—it works as a light lunch, dinner starter, or centerpiece at a summer table. The technique of draining tomatoes prevents a soggy filling, while brief, gentle cooking of shallots ensures they stay pale and sweet rather than caramelizing prematurely. Parmesan finish adds a sharp counterpoint. Serve warm or at room temperature with dressed greens.
Ingredients
- 1 ¾ cups all-purpose flour, plus extra to dust
- 1 tbsp English mustard powder
- 4 tbsp unsalted butter, chilled and chopped
- 2 oz lard, chilled and chopped
- 1 tsp thyme leaves, roughly chopped
- 1 medium free-range egg, separated
- 2 tbsp iced water, plus a little extra(optional)
- cream or whole milk, splash(optional)
- 1 lb tomatoes, not overly ripe
- 3 tbsp olive oil
- 6 ½ oz shallots, halved and finely sliced
- 1 tbsp Dijon mustard
- 1 tsp thyme leaves
- 1 oz Parmesan or veggie equivalent, coarsely grated
Instructions
- 1
Sift flour with mustard powder and salt, or whisk together.
- 2
Rub chilled butter and lard into flour with fingertips until mixture resembles coarse breadcrumbs with pea-sized bits remaining.
- 3
Stir in thyme.
- 4
Whisk egg yolk with iced water, trickle over flour, and cut in with a knife until combined, adding more water a little at a time as needed.
- 5
Gently knead pastry into a ball with your hands, wrap, and chill for at least 30 minutes.
- 6
Dust work surface with flour, roll pastry to about ⅓" thick into a circle, line the tart tin with excess overhanging, and chill for 20 minutes.
- 7
Heat oven to 350°F fan/gas 6.
- 8
Prick pastry base all over with a fork, line with baking paper, fill with raw rice or ceramic baking beans, place on a baking sheet, and bake for 15 minutes.
- 9
Remove paper and beans, whisk egg white with a little cream or milk, brush over base, and return to oven for about 10 minutes until completely cooked.
- 10
Remove and trim excess pastry from edges.
- 11
Slice off tomato tops, cut out cores, slice thinly, place in colander with salt, and drain.
- 12
Warm 2 tbsp oil in a frying pan over low-medium heat, fry shallots with salt until softened without coloring, stirring occasionally, for about 10 minutes.
- 13
Brush tart base with mustard, spoon shallots over top.
- 14
Layer tomatoes, scattering thyme, salt, and pepper as you go.
- 15
Trickle remaining oil over tomatoes.
- 16
Place tart tin on baking sheet and bake for 25-30 minutes until tomato tops begin to caramelize.
- 17
Remove tin, sprinkle parmesan over top, and return to oven for a further 5-10 minutes.
- 18
Serve warm or cold with green salad.
Tips
Keep all pastry ingredients ice-cold and work quickly to avoid melting the fat. This ensures a tender, flaky crust with distinct layers rather than a greasy, dense base.
Slice tomatoes uniformly thin and drain them thoroughly in a colander with salt for 15-20 minutes before assembly. This removes excess moisture that would otherwise make the filling soggy.
Cook shallots very slowly over gentle heat until barely softened, stirring regularly. Low temperature prevents premature browning and keeps them sweet and mild to balance the sharp mustard.
Good to Know
Covered in the refrigerator for up to 2 days. The pastry softens slightly; serve cold or reheat gently in a 160°C oven for 10 minutes.
Pastry dough can be made up to 2 days ahead, wrapped and chilled. Blind-baked shell keeps covered for 1 day. Assemble and bake on the day of serving for best texture.
Warm or at room temperature with a dressed green salad. Also works as a picnic dish served cold. Pairs with a crisp white wine or rosé.
Common Mistakes
Do not use warm butter or lard; they will melt into the flour instead of remaining as distinct pieces, resulting in a dense pastry rather than a flaky one.
Do not skip the tomato draining step. Wet tomatoes release moisture during baking, making the filling soggy and the pastry base damp.
Do not brown the shallots. High heat or neglect will cause them to caramelize too early, turning bitter and overwhelming the other flavors.
Substitutions
Dairy-Free Swaps
General Alternatives
FAQ
Can I make this tart ahead?
Yes. Prepare the pastry dough up to 2 days in advance and refrigerate it. You can also blind-bake the shell 1 day ahead and store it covered. Assemble and bake the filled tart on the same day for the best crispy-to-tender texture balance.
What if I don't have a loose-bottomed tart tin?
A standard tart tin works, though removal is trickier. Alternatively, use a rectangular tart tin or a 9-inch pie dish. Adjust baking time slightly if using a deeper vessel. Line the bottom with parchment paper for easier removal.
Why is my pastry tough or dense?
Overworking the dough develops gluten, toughening the crust. Mix gently and knead minimally. Using warm ingredients or melted fat instead of cold, chopped pieces will also cause density. Keep everything cold and handle briefly.