Why does my cake get hard after baking?
The first thing to check is if you are using the correct measurements. When a volumetric recipe says "cup", it usually doesn't mean "any cup in your cupboard", it means "a unit of measurement that is exactly 236 ml". This is so commonsense in the USA that nobody tells you about it, and for people from other countries, it comes as a great surprise. While using the wrong cup might scale the recipe proportionally, you still have the eggs to worry about here. 

The second thihng is that measuring by volume has a lot of leeway. Try weighing your solid ingredients instead. The conversion to try would be: 250 g flour, 100 g sugar, 115 g butter, 240 ml milk. Sift the flour before use. 

The third thing is to bake until done. Hard cakes often result from overbaking, and the time given is just a guideline. Test the cake every now and then, and take it out as soon as the tester shows no stickiness. Don't wait for the full 35 minutes (if they haven't happened yet) and don't let the cake stay in the oven for longer, even if you already turned it off. 

If you still dislike the results, turn to a cake recipe with less liquid, something that is closer to a traditional pound cake, with only a little extra liquid, or none at all.