Place 1 cup of sliced strawberries and ¼ cup of granulated sugar in a small saucepan. Use a masher or fork to break down the strawberries into a pulp.

Then heat the mixture over medium-low heat for a couple minutes while stirring frequently.

In a small bowl, combine 2 tablespoon water and 1 tablespoon cornstarch to make a cornstarch slurry. Pour into the strawberry mixture and continue to cook it until it becomes thick like jam, about 5 min.

Pour the mixture into a bowl and place in the fridge uncovered to cool.

Preheat the oven to 350 F / 175 C and line two large baking sheets with silicone baking mats or parchment paper.

In a large bowl or the bowl of a stand mixer, beat 1 cup butter and 1 cup granulated sugar and mix on a medium-high speed for a couple of minutes, until the mixture becomes lighter in color.

Mix in 3 tablespoon of strawberry reduction, 1 large egg + 1 egg yolk, 1 teaspoon vanilla extract, and a small drop of red gel food coloring (optional) until fully incorporated.

Add 2 ½ cups flour, 2 teaspoon baking powder, and 1 teaspoon fine salt, and mix on low speed until JUST incorporated.

Scoop 2 tablespoon of strawberry reduction onto the dough and use a knife to gently marble it in.

Roll dough balls in ¼ cup of granulated sugar and place on prepared baking sheets.

Bake for 10-12 minutes, until edges are set and centers are still soft. Cool for 15 minutes on the pan, then move to a wire rack.

Spread remaining strawberry reduction on cookies just before serving.