Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper.

For the base, combine flour, cocoa powder, brown sugar and salt in a medium bowl until evenly blended and no lumps remain. Add melted butter and stir to combine. Use your fingertips to evenly blend the mixture until it forms damp crumbs. Turn it out into prepared pan and press it down in an even layer. Bake for 10-15 minutes until slightly puffed and feels somewhat dry. Transfer to a wire rack to cool. Reduce oven temperature to 300°F.

For the filling, beat cream cheese until smooth. Beat in sugar until very silky and glossy. Beat in egg until well combined, then mix in vanilla and sour cream. Transfer half of this mixture to a bowl and stir in melted milk chocolate. Dollop the two mixtures alternately into the pre-baked crust and swirl together with a knife or skewer. Bake for 25-30 minutes until set around the edges and just slightly wobbly in center. Transfer to a wire rack to cool completely and then refrigerate for at least 2 hours.

For the glaze, combine cream, honey and salt in a small saucepan over medium heat and bring to a simmer. Remove from heat and add chocolate. Whisk until smooth and glossy. Stir in water one teaspoon at a time. Pour the glaze over chilled cheesecake and spread it out evenly. Refrigerate until set before slicing with a hot dry knife.