This recipe calls for Blackberry Sage Tea from The Republic of Tea company, but any berry-flavored black tea will work.
Preheat oven to 350 F. Combine flour, butter, salt, and sugar in food processor and blend until dough resembles cornmeal. Add just enough ice water to bring the dough together. Gather dough into a ball, flatten to a disk, wrap in plastic, and chill 30 minutes. Press into a 9- or 10-inch tart pan and generously prick the bottom with a fork. Bake at 350 F until golden brown, about 25 minutes.
While tart is baking, prepare pastry cream: Scald cream and milk by placing over medium heat until steam rises. Remove from heat. In a small bowl, combine eggs, sugar, and cornstarch. Whisk egg mixture quickly into the scalded liquid, then return to heat. Continue whisking until the mixture begins to simmer and thicken. Remove from heat immediately and stir in butter and vanilla. Cool, then spread in cooled, baked tart shell. Arrange assorted berries on top.
While the pastry cream and tart shell are cooling, prepare the Creme Anglaise: In a medium saucepan, heat milk and tea leaves, then remove from heat and let steep, covered, 15 to 30 minutes. In a separate bowl, whip together yolks and sugar on medium speed 4 to 5 minutes, until mixture is pale in color and doubled in volume. While eggs are mixing, reheat milk until steaming, then remove from heat. Whisk egg mixture into milk, stirring constantly. Return mixture to low heat, stirring constantly with a wooden spoon or heat-proof spatula, about 15 minutes, until the mixture coats the back of the spoon and has the consistency of thick gravy. Cool by placing saucepan in larger pot filled with ice cubes and cold water. Stir continuously until cooled, 10 to 15 minutes.
To serve, place tart slice on plate. Pour Creme Anglaise over slice and garnish with extra berries.