For the blueberry cake: Preheat the oven to 350 degrees F. Lightly butter a 9-inch springform pan and dust with flour.
Whisk 1 cup of the flour with the baking powder and salt in a medium bowl; set aside.
Combine the butter and sugar in a large bowl and beat with an electric mixer on medium-high speed until light and fluffy, about 3 minutes. Add the eggs one at a time, beating until well combined. Beat in the vanilla. Reduce the mixer speed to low and slowly add the flour mixture, beating until smooth. Spoon the batter into the prepared pan and smooth with an offset spatula. In a bowl, combine the berries with the remaining 1 teaspoon flour and the lemon juice, lemon zest and cinnamon; spoon over the batter.
Bake until golden and a toothpick inserted into the center comes out clean, about 50 minutes. Remove from oven and let cool in the pan for 10 minutes. Carefully slide a thin knife around the edges of the cake to release it from the pan. Transfer the cake to a platter, berry-side up, and dust lightly with confectioners' sugar.
For the lemon-mascarpone cream: In a medium bowl, whisk together the mascarpone and whipping cream until just combined. With a rubber spatula, fold in the honey, lemon zest and vanilla seeds.
To serve, spoon a dollop of the lemon-mascarpone cream on top of a slice of blueberry cake. (Refrigerate leftover cream in an airtight container for up to 2 days.)