1. Prepare the sugar cookie crust according to the recipe. Set it aside.

2. In a large mixing bowl, cream the softened butter until light and fluffy.

3. Add the egg yolks one at a time, beating well after each addition.

4. Gradually add the flour to the butter mixture, stirring until a dough forms.

5. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

6. Preheat your oven to 350°F (175°C) or 180°C.

7. Roll out the chilled dough on a floured surface to a thickness of about 1/8 inch.

8. Transfer the dough to a 9-inch tart pan with a removable bottom. Trim the edges and press the dough into the corners of the pan.

9. Prick the dough with a fork and line it with parchment paper. Fill with pie weights or dried beans.

10. Bake the crust for 20 minutes.

11. Remove the parchment paper and pie weights or beans.

12. In a separate bowl, whip the heavy cream until stiff peaks form.

13. Add the blueberries and raspberries, gently folding them into the whipped cream.

14. Spread the whipped cream mixture evenly over the baked tart crust.

15. Refrigerate for at least 30 minutes before serving.