• Preheat oven to 350 degrees F. Line an 8 x 8-inch baking pan with parchment paper.
• In a large bowl, whisk butter and sugars until smooth. Whisk in eggs and vanilla. Add flour, baking powder, and salt. Mix just until combined (do not overmix!). Fold in chopped white chocolate. Transfer batter to prepared pan.
• Bake until top is golden brown, about 25 to 30 minutes. Set pan on a wire rack, and let cool completely. Remove cake from pan and spread frosting in an even layer. Sprinkle with sea salt. Cut into 16 squares.

Raspberry Champagne Frosting

• Place raspberries and champagne in a small saucepan over medium heat. Bring to a boil, then reduce to medium low heat and continue cooking until reduced, about 6-8 minutes. Pass through a sieve and cool completely.
• Beat butter on high speed until light and fluffy. Mix in cooled raspberry/champagne reduction. Gradually add powdered sugar, beating at low speed until smooth.
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