Preheat the oven to 325°F (162°C). Grease a 9×9-inch stoneware baking dish. In a large bowl, use a hand mixer to beat together the butter and Besti until fluffy and light yellow. Beat in the eggs, cream, and vanilla. Beat in the almond flour, baking powder, and sea salt until uniform. The batter will be fairly thick. In a small bowl, stir together the almond flour, Besti Brown, cinnamon, and sea salt until uniform. In another small bowl, stir together the melted butter and vanilla. Add the melted butter mixture to the brown sugar mixture and stir until crumbly. Spread half of the coffee cake batter evenly over the baking dish. Crumble half of the streusel (about 1.5 cups) on top. Dollop tablespoonfuls of remaining batter over the streusel, then spread evenly. Crumble remaining streusel on top. Bake for about 25 minutes, until the streusel is darker golden. Tent the top with foil and bake for 20-30 more minutes, until the coffee cake is no longer jiggly and an inserted toothpick comes out clean. Whisk together the Besti Powdered and heavy cream. Allow the cake to cool for at least 20 minutes before drizzling with icing.