Preheat oven to 350ºF. Put the blueberries in the small bowl and toss with the 1 tablespoon of flour. If you are using a mix of fruits and they vary in degree of softness, separate them for this step.
Spoon the remaining flour into the first large bowl. Add the baking powder, baking soda and salt, and gently stir together with a fork.
In the other large bowl, beat the butter (or butter/plant butter mixture) with a hand mixer until it is smooth, then add the sugar and beat until it becomes fluffy (this is where you see how the plant butter acts the same as regular butter—it’s pretty cool to see).
If your mix includes vegetable oil, add it now; then beat in the eggs, one by one, mixing well between each one. Then add the lemon juice and the vanilla and combine. Gradually beat in the flour mixture, alternating with the buttermilk. When that step is complete, mix in the fresh rosemary.
Finally, carefully fold in the berries, by hand.
Lightly oil the bundt pan, then spoon the batter into it.
Bake the cake at 350ºF for 45 to 50 minutes—in our oven, this was done at about 45 minutes. A tester slid into the center should come out clean.
Cool the cake for 20 to 30 minutes on a rack. Loosen the edges carefully with a thin knife, then turn it out of the mold onto a sizable plate.
Glazing the cake. If you intend to glaze this, wait until it is completely cool. Stir the confectioners sugar and lemon juice together in a bowl until the sugar completely dissolves and there are no lumps. Spoon the glaze over the cake.
I used my usual glaze recipe, and waited for several hours before glazing, but for some reason the glaze refused to be visible. The photo you see here does show this cake with glaze on it—it is apparently my famous invisible glaze—who even knows any more? Honestly, this cake is so sweet and likeable that I don’t think it really needs a glaze. But adding the glaze ramps things up a notch and keeps it moist and tender for an extra day.