Start the strawberry reduction by adding the sliced strawberries into a food processor and pulse until you have about 1 ½ cups puree.
Add the puree into a medium saucepan and heat over medium-high heat, stirring often, until thickened and reduced by about half. This should take about 20 minutes.
Set the reduction aside to cool.
Preheat the oven to 350°F (180°C), or 160°C for a fan oven. Grease and flour a 9x13 inch (22x33 cm) baking pan and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, add the butter and granulated sugar and beat until light and fluffy. Add the eggs, one at a time, beating well after each addition. Add the cooled strawberry reduction, vanilla extract, and pink food coloring. Mix well.
Add half the flour, mix until just combined. Add the sour cream, mix well, then add the remaining flour and mix until combined. Add the milk and stir well. Pour the batter into the prepared pan and bake in the preheated oven for 28-32 minutes, or until a toothpick inserted in the center comes out clean.