Add the butter, granulated sugar, and brown sugar to a mixing bowl and beat until fluffy and creamy.
Mix the eggs into the bowl one at a time until smooth.
Place the flour, baking powder, milk, and vanilla extract in the bowl and beat until just combined.
Fold the pecans and toffee chips into the batter.
Grease the inside of a bundt pan and fill it with the batter. Smooth the top out and bake for 1 hour and 30 minutes, or until cooked completely through.
Remove the cake from the oven, turn over and allow to cool on a rack.
When the cake has cooled, add the evaporated milk and 1 cup of brown sugar to a saucepan over medium-high heat on the stove. Bring the mixture just to a boil and then reduce to simmer for 8-10 minutes.
Remove the mixture from the heat and stir in the butter and vanilla extract.
Drizzle the sauce while still hot over the cooled cake and serve.