Heat oven to 350°F (177ºC) with rack set in middle position. Lightly grease a 9-inch round pan (or 8-inch square pan); line bottom of pan with parchment paper.
In a stand mixer fitted with paddle attachment, beat together 8 tablespoons butter, ¾ cup (150g) sugar, 1 teaspoon baking powder, ¾ teaspoon salt and ½ teaspoon nutmeg on medium speed until smooth, about 1 minute; scrape down sides of bowl.
Beat in 2 eggs, one at a time, scraping down bowl after each addition.
Stir in 1 teaspoon vanilla and ½ teaspoon lemon zest. With mixer on low speed, gradually add 1 cup (130g) flour until a stiff batter is formed. Scrape down sides of bowl and give batter a few mixes by hand to ensure no pockets of dry flour remain.
Spread batter into prepared pan. Sprinkle 1 cup berries evenly over top. Combine remaining 2 tablespoons sugar and ¼ teaspoon cinnamon and sprinkle over fruit.
Bake cake until a toothpick inserted in center comes out clean and top of cake is light golden brown, 35–40 minutes. Transfer to a wire rack and cool, in pan, for 10–15 minutes.
Run a paring knife or offset spatula around edges of pan to loosen cake. Place a wire rack over top of pan and gently flip pan to release cake. Place a second wire rack on top of cake and flip again so top is facing up. Serve warm or at room temperature.