Step 1: Prepare the Cake

1. Preheat oven to 350°F (175°C). Grease and flour two 9-inch cake pans.
2. In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
3. In a large bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition.
4. Mix in vanilla extract, lemon zest, and lemon juice.
5. Gradually add the dry ingredients to the butter mixture, alternating with buttermilk, beginning and ending with the flour mixture. Mix until just combined.
6. Divide the batter evenly between the prepared cake pans and smooth the tops.
7. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.
8. Let cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Step 2: Make the Strawberry Filling

1. In a small saucepan over medium heat, combine strawberries, sugar, and lemon juice.
2. Cook for about 5 minutes until strawberries soften and release their juices.
3. Stir in the cornstarch mixture and cook for another 2 minutes until the filling thickens.
4. Remove from heat and let cool completely.

Step 3: Prepare the Lemon Buttercream Frosting

1. In a large bowl, beat butter until creamy.
2. Gradually add powdered sugar, beating well after each addition.
3. Mix in lemon juice and vanilla extract.
4. Add heavy cream one tablespoon at a time until the frosting reaches a smooth, spreadable consistency.

Step 4: Assemble the Cake

1. Place one cake layer on a serving plate. Spread a layer of lemon buttercream on top.
2. Spoon the cooled strawberry filling over the buttercream.
3. Place the second cake layer on top and frost the entire cake with the remaining buttercream.
4. Decorate with fresh strawberries, lemon slices, and mint leaves if desired.