• Preheat the oven to 350°F. Grease and flour two 8” cake pans.
• In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
• In a large bowl, cream the butter and sugar on medium-high speed for about 2–3 minutes, until light and fluffy.
• Beat in the eggs one at a time, mixing well between each.
• Add vanilla, lemon extract, and lemon zest.
• Add the lemon juice.
• With mixer on low, alternate adding the flour mixture and buttermilk in 3 additions, starting and ending with the dry.
• Mix just until combined — don’t overmix.
• Divide evenly between the pans and bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
• Let cool in pans for 10 minutes, then turn out onto wire racks to cool completely.

Filling

• In a small saucepan over medium-low heat, whisk milk, flour, and salt constantly until thick like pudding.
• Remove from heat.
• Stir in vanilla and lemon extract. Let cool completely to room temp.
• Using a mixer, beat butter and sugar for about 5 minutes, until very fluffy and light.
• Add the cooled milk mixture and beat for another 5 minutes, until light and fluffy.
• Spread over the bottom cake layer (leave a slight border) and top with the second layer (flat-side up for a smooth top).

Frosting

• Beat butter until pale and fluffy (about 3–4 minutes).
• Gradually add powdered sugar, mixing on low at first.
• Pour in melted white chocolate and beat until smooth.
• Add extract and cream if needed to adjust texture.
• Chill for 10–15 minutes if it's too soft, then spread onto the cake with an offset spatula.