Place the sugar and softened butter in a mixing bowl.

Beat with a hand mixer for two to three minutes, until smooth.

Add the almond flour.

Add the eggs, one at a time.

Beat until the eggs are fully incorporated.

Add the oat milk and gluten-free flour.

Beat until the mixture is smooth and even.

Finally, add the pistachio paste.

Mix until fully combined.

Mix the flour with the remaining dry ingredients on a work surface or silicone pastry mat.

Make a well in the center.

Add the vegan butter and eggs.

Work the mixture with your fingertips or a pastry cutter until the dough is sandy.

Briefly knead until the dough just comes together.

Shape it into a ball.

Wrap it in plastic wrap.

Refrigerate for 1 hour.

Roll out the chilled dough between two sheets of parchment paper.

Aim for a thickness of 3-4 mm, using dough thickness guides for an even result.

Prepare a 20 cm cake ring or a 20 cm springform pan, 4 cm deep.

Carefully transfer the dough to a tart ring or cake pan.

Press it into the corners and up the sides.

Check the base for any holes.

Trim the edges.

Refrigerate for 10 minutes to let the dough rest.

Fill the chilled tart shell with the pistachio-almond frangipane.

Smooth the top with a spoon or offset spatula.

Bake in a preheated 185°C oven for 18 to 20 minutes.

Transfer the baked tart to a wire rack.

Let cool to room temperature.

Remove the cake ring.

Transfer the tart to a cake board or serving plate.

Spread the raspberry jam over the cooled tart.

Arrange the raspberries upside down over the top, covering the tart completely.

Sprinkle with chopped pistachios.

Refrigerate for 30 minutes before slicing and serving.