To prepare cupcakes, preheat over to 375F. Grease muffin tin or line with muffin liners. In a large bowl, sift flour, baking powder, baking soda and salt. Mix well. In the bowl of an electric mixer fitted with the paddle attachment, cream butter on medium-high speed, until light and fluffy. Gradually add sugar and continue to beat until well combined and fluffy. Reduce the mixer speed to medium and slowly add eggs until just blended. With the mixer on low, slowly add half the flour mixture; mix until just blended. Add the milk and vanilla extract, mix until just blended. Slowly add remaining flour mixture, scraping down sides of the bowl with a spatula, as necessary, until just blended. Divide batter evenly among prepared muffin cups. Transfer muffin tin to oven and bake for 25 minutes, or until just lightly golden on edges and knife inserted into the center comes out clean. Transfer muffin tin to a wire rack and let cupcakes cool completely. To prepare buttercream, beat butter for a few minutes in a standing mixer with the paddle attachment on medium speed. Add powdered sugar and turn your mixer on low, beat until the sugar incorporates with the butter. Add vanilla, heavy cream and strawberry puree, beat on medium speed for another 3 minutes, or until buttercream becomes light and fluffy. Frost the cupcakes with the buttercream and garnish with strawberry slices.