In a large mixing bowl, beat the softened salted butter and granulated sugar together until light and fluffy, about 2 to 3 minutes. This creaming step is important for creating a tender muffin so do not rush it.

Add the eggs one at a time, mixing well after each addition until fully incorporated. Add the vanilla extract and lemon zest and mix until combined.

In a separate bowl, whisk together the oat flour, baking powder, poppy seeds, and sea salt until evenly combined.

Add the dry mixture to the wet mixture in three additions, alternating with the almond milk. Start and end with the dry mixture. Stir gently between each addition just until combined. Do not overmix or the muffins will be dense rather than tender.

Divide the batter evenly between the 12 lined cups, filling each one about two thirds full. The batter will rise as it bakes so do not overfill.

Bake for 30 to 35 minutes until the tops are lightly golden and a toothpick inserted into the center of a muffin comes out clean.

Allow the muffins to cool in the pan for 10 minutes before transferring to a wire cooling rack. They will continue to set as they cool so give them the full time before handling.