Preheat your oven to 180°C (350°F). Prepare a 15 cm (6″) round baking pan by lining it with parchment paper or greasing and flouring it. In a medium bowl, whisk together the flour, baking powder, and baking soda, then set this mixture aside. In the bowl of a stand mixer, combine the sugar, eggs, and salt. Beat them together on high speed for at least 10 minutes until the mixture is pale, thick, and airy. In a separate bowl, mix together the buttermilk, oil, strawberry purée, and food coloring (if using). Note that without food coloring, the cake will have a brownish tone rather than a vibrant pink. Turn your mixer to its lowest speed and slowly pour the liquid mixture into the whipped eggs and sugar. Add the liquid gradually, mixing for 30–60 seconds until just incorporated.