Preheat oven to 350°F (175°C). Grease and flour an 8-inch round cake pan. In a bowl, whisk gluten-free flour, baking powder, baking soda, and salt. In a separate large bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Mix in vanilla extract and sour cream. Gradually add dry ingredients alternating with milk, beginning and ending with dry ingredients. Mix until combined. Fold in chopped strawberries gently. Pour batter into prepared pan and smooth the top. Bake for 35-40 minutes or until a toothpick inserted in the center comes out clean. Let cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.