1. Combine flour, powdered sugar, and salt, then cut in cold butter until the mixture resembles coarse crumbs. Mix in a whisked egg yolk and vanilla extract until the dough just comes together, then form into a disk, wrap, and chill for at least 30 minutes.

2. Preheat oven to 375°F (190°C). Roll out the chilled dough to 1/8-inch thickness, cut circles, and press them into a mini tartlet pan. Prick the bottoms with a fork.

3. Bake the shells for 10-12 minutes until lightly golden, then let them cool completely on a wire rack.

4. To make the ganache, place chocolate chips in a heatproof bowl. Heat heavy cream until just simmering, then pour it over the chocolate. Let sit for 5 minutes before whisking until smooth and glossy.

5. Cut large marshmallows in half diagonally to create ear shapes. Press the sticky, cut side into pink sanding sugar to create the inner ear.

6. Pour the slightly cooled ganache into the cooled tartlet shells. Gently place two marshmallow bunny ears on top of each tartlet.

7. Allow the tartlets to set at room temperature for about an hour or in the refrigerator for 20-30 minutes until the ganache is firm.