Buttery pastry, soft almond cream, and red plums baked until they're sweet and slightly jammy. The frangipane puffs up around the fruit, going golden at the edges. Dust it with icing sugar and you've got a proper French tart to make in late summer when plums are everywhere.
Roll the chilled pâte sablée out to about 3mm and line your tart ring, set on a baking mat. Trim the edges and prick the base with a fork. Chill for 20 to 30 minutes while you make the frangipane.
2. Make the frangipane
Beat the butter and sugar until pale, about 2 minutes. Add the eggs one at a time, beating between each. Add the ground almonds and rum and mix just until smooth. Don't overwhip.
3. Assemble
Heat the oven to 180°C (160°C fan). Spread the frangipane over the base, just below the pastry rim. Press the halved plums in, cut-side up, arranged evenly.
4. Bake
Bake for 35 to 40 minutes, until the frangipane is set and deep golden and a skewer in the centre comes out clean. The plums should be soft and jammy at the edges. Cover loosely with foil if the top browns too fast.
5. Glaze and cool
Brush the warm tart with warmed apricot jam for a glossy finish, if using. Cool completely in the tin before unmoulding.
6. Serve
Dust with icing sugar and serve with crème fraîche or vanilla ice cream.
Notes
Ripe but firm plums hold their shape and don't flood the tart. Overripe ones release too much juice.
Arrange them cut-side up to hold the juices in and colour nicely.
Don't overwhip the frangipane, or it puffs and sinks. Beat just until smooth.
Keep the frangipane below the rim. It rises as it bakes.
Make ahead: pastry and frangipane both keep days in the fridge or a month frozen. Assemble and bake fresh.