Combine the flour, sugar, and salt in a large mixing bowl. Add the cold, cubed butter and use a pastry cutter or your fingertips to work the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces. Add the egg and mix until the dough comes together. Press the dough into a disc, wrap in plastic, and chill in the refrigerator for 30 minutes.
Preheat the oven to 375°F (190°C). Remove the chilled dough from the fridge and roll it out on a lightly floured surface to fit your tart pan. Transfer the dough to the pan, pressing into the edges and trimming any excess. Prick the bottom with a fork several times.
Line the tart crust with parchment paper and fill with pie weights or dried beans. Bake on a baking sheet for 15 minutes, then remove the weights and parchment and bake for an additional 10-15 minutes until golden brown. Let the crust cool on a wire rack.
In a saucepan, heat the heavy cream until just simmering. In a bowl, whisk together the sugar, egg yolks, and cornstarch until smooth. Slowly pour the hot cream into the egg mixture, whisking constantly to prevent curdling. Return the mixture to the saucepan and cook over medium heat until thickened and bubbling, about 5 minutes. Remove from heat and pour into the cooled tart shell, smoothing the surface.
Arrange the fresh berries over the custard in an attractive pattern. If desired, gently warm honey and brush over the berries for shine. Chill the tart in the refrigerator for at least 1 hour before serving to allow the custard to set.
Just before serving, drizzle with honey or glaze if using, and optionally garnish with fresh mint leaves. Slice and serve directly from the tart pan or transfer to a platter for presentation.
