To make the chocolate sauce, finely chop the Lindt EXCELLENCE 70%. Transfer to a heat-safe bowl set over saucepan of barely simmering water for 5 minutes or until the chocolate has melted and can be stirred. Don’t let the water touch the bowl while the chocolate is melting.
Heat the remaining sauce ingredients in a saucepan on a low heat until combined. Remove from the heat and stir in the melted chocolate. Set aside.
To make the milkshake, put the whole milk and chocolate ice cream into a blender and blend until smooth. Transfer the mixture into two glasses
Place brown sugar, granulated sugar and eggs in the bowl of a stand mixer fitted with the paddle attachment. (Alternatively, use a large bowl with electric hand mixer). Beat on high speed until light and fluffy and doubled in size, scraping down sides of the bowl as needed, 3-4 minutes. Beat in vanilla extract. Beat in butter and chocolate mixture until smooth. Add flour, cocoa and salt to batter and beat until just combined.
Assembly: Top the milkshakes with whipped cream and drizzle with the chocolate sauce. Garnish with raspberries before serving.