1. Make the Lemon Cake:

1. Preheat oven to 350°F (175°C). Grease and flour three 8-inch (20cm) round cake pans.
2. In a bowl, whisk together flour, baking powder, and salt.
3. In a large bowl, cream butter and sugar until light and fluffy (about 3-4 minutes).
4. Add eggs one at a time, beating well after each. Mix in lemon zest, lemon juice, and vanilla.
5. Add flour mixture in three parts, alternating with milk, beginning and ending with flour. Mix until just combined.
6. Divide batter evenly among pans. Bake for 22–25 minutes, or until a toothpick comes out clean.
7. Cool cakes in pans for 10 minutes, then turn out onto a rack to cool completely.

2. Make the Strawberry Filling:

1. Combine strawberries, sugar, and lemon juice in a saucepan over medium heat.
2. Cook, stirring, until strawberries release their juices and soften (about 5–7 minutes).
3. Stir in the cornstarch slurry and cook until thickened (1–2 minutes).
4. Remove from heat and let cool completely.

3. Make the Lemon Buttercream:

1. Beat butter until creamy.
2. Gradually add powdered sugar, beating well after each addition.
3. Add lemon juice, lemon zest, and salt. Beat until smooth.
4. Add cream as needed to reach desired consistency.

4. Assemble the Cake:

1. Place one cake layer on a serving plate. Spread with half the strawberry filling.
2. Add the second cake layer and top with remaining filling.
3. Add the third cake layer. Frost the top and sides with lemon buttercream.
4. Decorate with fresh strawberries and lemon slices if desired.