1-First, cream the 10 tablespoons of cold unsalted butter and 1/2 cup granulated sugar until they are light and fluffy; this usually takes a few minutes with a mixer.

2-Next, add one whole egg and the yolk of the second egg, then pulse to combine everything evenly.

3-Add the 2 cups of all-purpose flour and 1/4 teaspoon fine sea salt, pulsing until the dough forms a ball; if it’s too dry, mix in the reserved egg white.

4-Once the dough is ready, flatten it into a disk and chill for 10-20 minutes to keep its texture perfect.

5-Roll out the dough slightly larger than a 9 or 10-inch tart pan, transfer it into the pan without stretching, press it into the sides and bottom, and chill again for a bit.

6-Now, preheat the oven to 350°F (180°C) for the filling.

7-Toss the 2 cups fresh blueberries, 1 cup fresh sliced strawberries, zest and juice of 1 lime, 2 tablespoons granulated sugar, and 2 tablespoons all-purpose flour together in a bowl.

8-Spoon this mixture into the chilled tart shell and dot with the 1 tablespoon butter pieces.

9-Bake for 1 to 1 hour and 20 minutes until the shell is light golden and the fruit is set, then cool on a rack for about 1 hour.

10-Before serving, warm the 2 tablespoons of fruit jam and brush it over the tart for a glossy finish.

11-Serve with ice cream or whipped cream for an extra treat.