Purée the blackberries in a blender; strain if you prefer a smoother texture. Measure 1 cup purée.

Bloom the gelatin: sprinkle ¾ tsp gelatin over 1 ½ tsp water; let sit 5 minutes.

In a small saucepan, combine the purée, ½ cup sugar, 1 tbsp cornstarch, and a pinch of salt. Whisk until smooth.

Cook over medium heat, stirring constantly, until the mixture thickens and just comes to a boil, about 3–4 minutes.

Remove from heat. Stir in bloomed gelatin and 1 tsp lemon juice until dissolved. Cool to room temperature, then chill until slightly set.

In a saucepan, heat 2 cups milk with the split vanilla bean and 2 Earl Grey tea bags. Bring just to a simmer, then remove from heat. Steep 8–10 minutes, covered.

Whisk 4 egg yolks with ½ cup sugar, 4 tbsp cornstarch, and a pinch of salt until pale and smooth.

Remove tea bags and vanilla pod from the milk. Slowly temper the yolk mixture by whisking in about ½ cup hot milk, then pour the tempered mixture back into the saucepan.

Return to medium-low heat and whisk constantly until it thickens to a pudding-like consistency and comes to a gentle simmer, about 2–3 minutes.

Remove from heat. Whisk in 2 tbsp butter until glossy. Strain through a fine-mesh sieve into a bowl. Press plastic wrap directly on the surface to prevent skin. Chill until firm, at least 2 hours.

In a bowl, whisk 1 ½ cups flour, ½ cup sugar, and 1 tsp kosher salt.

Cut in 1 stick cold butter (diced) with a pastry cutter or fingertips until the mixture resembles coarse crumbs with pea-sized bits.

Stir in 1 egg yolk and 3 tbsp cold water just until the dough comes together. Don’t overwork it.

Form into a disk, wrap, and chill at least 30 minutes.

Roll out on a lightly floured surface to about 1/8-inch thick. Line tart pans or a 9-inch tart pan, trim edges, and dock the bottoms with a fork.

Chill lined shells 15 minutes. Preheat oven to 375°F (190°C). Blind bake with parchment and weights for 15 minutes, remove weights and bake 5–8 minutes more until golden. Cool completely.

Spoon chilled pastry cream into each tart shell, smoothing the top.

Dollop or pipe the blackberry filling in small pools across the cream, then use a skewer to create pretty swirls or marbling.

Chill to set (30–60 minutes).

Whip ¾ cup heavy cream to soft peaks; sweeten lightly if desired. Pipe or spoon onto tarts and garnish with fresh blackberries. Serve cold.