Homemade Strawberry Cake with Strawberry Filling

Strawberry reduction
1 In a medium saucepan over medium heat, add the strawberries, sugar, and lemon juice.
2 Stir occasionally and let the strawberries release their juices for about 5-7 minutes.
3 Use a fork or potato masher to break them down further as they soften.
4 In a small bowl, mix the cornstarch with the cold water until smooth. Slowly pour into the saucepan while stirring constantly.
5 Let the mixture simmer for 3-5 minutes, stirring frequently, until thickened. You should have around 2 cups of strawberry reduction. Cool completely before using.
Strawberry Cake
7 Preheat the oven to 350 F. Grease the sides and line the bottom of three 8-inch round cake pans with parchment paper.
8 In a separate bowl, whisk together the dry ingredients: flour, baking soda, baking powder, and salt.
9 In a large mixing bowl with the paddle attachment, beat the oil and sugar with an electric mixer on high speed for one minute, then reduce to medium speed. Add eggs one at a time, mixing between each. Stir in vanilla and food coloring if using.
10  In a separate bowl, mix the buttermilk with ¾ cup of strawberry reduction. 
11 Switch the mixer to low speed. Add the dry ingredients to the wet ingredients, alternating with the strawberry buttermilk, beginning and ending with flour. Mix until just combined.
12 Divide the cake batter between the prepared cake pans and smooth the tops. Bake for 23-28 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 15 minutes before transferring to a wire rack to cool completely.
Strawberry Buttercream Frosting
14 Beat butter on medium speed for 2 minutes until smooth. Mix in vanilla extract and salt.
15 Gradually add sifted powdered sugar, one cup at a time, mixing on low speed.
16 Add the strawberry reduction and beat until fully incorporated. Do not overbeat! If your frosting is too soft, the layers won't support the filling.
17 If the buttercream is too thin, add a little more sifted powdered sugar until reaching the desired consistency.
Assembly
19 Level the cooled cake layers for even stacking.
20 Place a small amount of buttercream on a cake stand and add the first cake layer.
21 Spread a thin layer of buttercream on top, then use a piping bag or a zip-lock bag with the tip cut off to pipe a buttercream border around the edge, forming a barrier. This will help contain the strawberry reduction filling and keep it from spilling over the sides of the cake.
22 Fill the center with half of the remaining strawberry reduction, making sure it stays within the border. 
23 Place the second cake layer on top of the first, making sure they align. Repeat the process with the second cake layer, filling it with the remaining strawberry filling. 
24 Place the third layer on top and cover the entire cake with a thin layer of buttercream (crumb coat). Refrigerate for 30 minutes to let the filling and crumb coat set.
25 Frost the entire cake with the remaining buttercream, using the back of a spoon to create swirls and smoothing the sides and top.
26 Garnish with fresh strawberries on top of the cake for the final touch.