Preheat oven to 350 degrees F (175 degrees C). Grease and flour an 8-inch round cake pan.
Sift flour, baking powder, and salt in a large bowl.
Heat a skillet over medium heat. Add pumpkin seeds and cook, stirring frequently, until lightly brown and toasted, about 5 minutes. Pour into a food processor. Blend the toasted pumpkin seeds in the food processor until sand-like in texture. Add to the flour mixture.
Place ground flax seeds in the same skillet. Cook and stir until toasted, about 4 minutes. Mix into the flour mixture until well combined.
Beat butter and sugar together in a bowl using an electric mixer until light and fluffy. Add eggs, 1 at a time, and vanilla extract, mixing until well combined. Add the flour-seed mixture in batches, alternating with milk, beating batter briefly after each addition until batter is fully blended. Pour batter into the prepared pan.
Bake in the preheated oven until a toothpick inserted into center of the cake comes out clean, 35 to 40 minutes.