**Instructions:**

1. **Prepare the Dough:**
– In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy.
– Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
– In a separate bowl, whisk together the flour, baking powder, and salt.
– Gradually add the dry ingredients to the wet ingredients, mixing until a soft dough forms.

2. **Shape and Bake the Cookies:**
– Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
– Roll the dough into small balls (about the size of a walnut) and place them on the prepared baking sheet.
– Bake for 12-15 minutes, or until the bottoms are lightly golden. The tops should remain pale.
– Remove from the oven and let them cool completely on a wire rack.

3. **Prepare the Filling:**
– Mix the pastry cream or vanilla custard with the peach jam until well combined.
– Once the cookies are cool, hollow out a small cavity in the bottom of each cookie using a small spoon or a melon baller.

4. **Assemble the Peach Cookies:**
– Fill the cavity of each cookie with the prepared filling and sandwich two cookies together to form a peach shape.
– In a small bowl, mix the milk with the peach liqueur (if using). Divide the mixture into two bowls and add red food coloring to one and yellow food coloring to the other.

5. **Decorate the Peaches:**
– Lightly dip one side of the sandwiched cookies into the red coloring and the other side into the yellow coloring to resemble a peach.
– Roll the colored cookies in granulated sugar to coat them evenly.

6. **Garnish and Serve:**
– Garnish each peach cookie with a fresh mint leaf to resemble a peach leaf.
– Arrange the peach cookies on a platter and serve.